Elderflowers, strawberry and rhubarb mousse cake

Instructions

Pistachio sponge biscuit

1. Preheat the oven to 160°C, ventilation mode. Line a baking tray with a 25x20 cm mould, greased and covered with parchment paper.
2. Melt the butter in the microwave and set aside to cool slightly down (45°C). In the bowl of the freestanding mixer fitted with paddle attachment combine together egg yolks, eggs, 45 g of caster sugar,  pistachio paste, lemon zest and salt and work until obtain a smooth batter. Add in the melted, lukewarm butter little by little and, once blended, add in the pistachio flour mixed with the whole wheat flour. Work until obtain a smooth, homogeneous batter.
3. In the bowl of the freestanding mixer fitted with whisk attachment beat the egg whites just until a bit foamy (not stiff peaks). Add slowly and little by little the 52 g of caster sugar and beat until obtain a shiny meringue.
4. Add a small part of the meringue into the batter and fold vigorously with a spatula to soften the batter. Then fold gently the meringue into the batter in two times using always the spatula.
5. Transfer the mixture into the mould, spread it out evenly with a palette knife and bake for approximately 20 min, until slightly golden. Set aside to cool down, then put in the freezer for about 1h to let it get cold completely.
6. Cut out the cold biscuit with a 16 cm stainless steel cake ring, wrap it with clingfilm and store in the freezer.

Pistachio crumble

1. Preheat the oven to 160°C, ventilation mode. Place all the ingredients into a small grinder and mix until obtain a sandy mixture.
2. Spread the crumbs on a perforated tray lined with a Silpat mat and place in the freezer for 30 minutes.
3. Bake the crumble for about 15 minutes, until golden-brown. Take out of the oven and dust with cocoa butter powder (Mycryo) to preserve crunchiness. You can store any leftover crumble in an airtight container.

Pistachio croustillant

1. Melt the white chocolate in the microwave to 45°C.
2. Add the pistachio paste and stir with a spatula.
3. Roughly chop the shelled pistachios with a small food processor or grinder then add into the mix of white chocolate-pistachio paste, followed by the pistachio cumbles. Combine well with a spatula to obtain an uniform and grainy mixture.
4. Spread the croustillant on the base of the frozen cake with a small palette knife about 3 mm thick and place in the freezer. Store the leftover croustillant in an opaque airtight container to room temperature and away from light.

Strawberry-rhubarb confit

1. Slice the rhubarb stalk into approximatively 1 cm chunks, then place the pieces into a saucepan and add 52 g cane sugar. Stir well with a spatula to coat the rhubarb with the sugar and set aside to room temperature for 30 minutes, so that rhubarb releases its juices.
2. Add the strawberries puree and bring to boil. Once boiling, cook for 5 minutes on moderate heat, until the rhubarb is soft. Add the natural red food coloring to enhance the color of the confit and blend with a hand blender to break up the rhubarb pieces and to obtain a smooth mixture.
3. Mix the remaining 52 g cane sugar with the pectin NH and add into the strawberry-rhubarb mixture. Bring to boil again and cook for 1 minute by stirring continuously with a spatula.
4. Remove from the heat and add in the lime juice and the lemon juice and stir with the spatula.
5. Pour into a 16 cm round silicone mould to 1cm thick and freeze for at least 2h.

Strawberry Inspiration crémeux

1. Soak the gelatin sheets in cold water.
2. Melt the couverture in the microwave to 45°C.
3. Heat the strawberries puree with the glucose in the microwave without boiling, then add the soaked gelatin sheets and stir with a spatula to dissolve the gelatin.
4. Pour the strawberries puree in one step over the melted couverture and stir vigorously with a spatula to obtain a smooth cream.
5. Transfer the cream into a mixing glass and emulsify with the hand blender to obtain a glossy and velvety texture. Add slowly and to wire the cold heavy cream, blending continuously with the mixer and without adding air bubbles.
6. Pour over the frozen confit to 1cm thick and place in the freezer for 2h.

Elderflowers and vanilla mousse 

1. Soak the gelatin sheets in cold water. Close the base of a stainless steel cake ring (18 cm wide and 6 cm high) with a sheet of clingfilm, ensure that the clingfilm is well stretched and flat to avoid marks in the mousse. Place the ring onto a tray lined with a Silpat mat and arrange an acetate strip (18 cm length and 6 cm high) inside the ring.
2. Melt the white chocolate to 45°C in the microwave. Heat also the elderflowers syrup in the microwave without boiling, add the drained gelatin sheets and stir with a spatula to dissolve.
3. Pour the elderflowers syrup over the chocolate, in three times, stirring with a spatula just to obtain a velvety, glossy cream.
4. Pour the cream into a mixing glass, add the vanilla seeds and mix with the hand blender to obtain the best and most silky smooth consistency. Pour the cream in a bowl and cool down to 35-40°C.
5. Semi-whip the heavy cream and fold it gently into the lukewarm white chocolate cream.
6. Pour about half mousse into the ring. Insert the frozen confit-crémeux insert (with the Strawberry Inspiration crémeux facedown) and press gently and slightly down. Cover the insert with the remaining mousse and finally place the pistachio sponge biscuit (with the cake facedown and the pistachio croustillant upwards). Press it gently and slightly down until it is level with the mould. Clean any excess mousse with a palette knife. Freeze for approximately 4-6 hours in a domestic freezer or 90 minutes in a blast freezer.
7. Unmould the frozen cake by warming up the edges of the ring with your hands and store the cake in the freezer with both the clingfilm and the acetate strip.

Mirror glaze 

1. Soak the gelatin sheets in 58 g cold water for at least 10 min.
2. Heat the heavy cream in the microwave to 40°C, add the skimmed milk powder and stir with a fine whisk to dissolve the milk powder.
3. Heat 72 g water, caster sugar and glucose syrup in a saucepan to 110°C, stirring occasionally with a spatula.
4. Remove from the heat and pour in the lukewarm heavy cream. Pour into a measuring cup or mixing glass, cover with clingfilm pressed on top of the glaze and put briefly in the fridge to cool down.
5. Once the glaze is 60°C, add the soaked gelatin sheets, the Absolu Cristal and the grape seed oil. Emulsify with a hand blender, without adding air, to obtain a smooth and shiny glaze.
6. Finally add in the red food coloring and emulsify once again for about 1 minute.
7. Strain the glaze to remove any possible bubbles, cover with clingfilm touching the surface and place in the fridge for at least 12h (overnight).
8. Heat the glaze in the microwave until the edges start to melt. Transfer into a mixing glass and emulsify with the hand blender, so that the centre begins to melt too. Keep the blade of the hand blender on the bottom of the mixing glass to avoid adding air.
9. Set the frozen cake on a 14 cm cake ring with a pair of clingfilm sheets underneath, to collect the excess glaze.  Peel away both the clingfilm on top of the cake and the acetate strip around the edge of the cake. Cover the cake with the glaze at 30-32°C (inasmuch the glaze has a pale rose color, the edges of the cake will be cover with a thin and quite transparent layer of glaze). Wipe off any excess glaze on top of the cake with a large flat palette knife, angling it slightly and lifting it up at the edge. When the glaze stops dripping, remove any excess glaze from the base with a small sharp knife. Place the finished cake onto a plate and place in the fridge. The leftover mirror glaze can be stored in the fridge for up to 3 weeks or freezer for 2 months and re-heated and adjusted with water if needed.

Assembly and decoration

1. For both the Ruby chocolate flexible band around the cake and the thin Ruby chocolate rings on top of the cake you need to temper Ruby chocolate (here the method). The temper chocolate curve is 45°C (melting) - 26°C (cooling) - 28/29°C (usage).
2. Make the Ruby chocolate flexible band: grease slightly the work surface with a non-stick spray or a bit of butter and stick an acetate strip of 60 cm length and 3 cm high. Pour a line of tempered Ruby chocolate lengthwise and smooth the surface of the chocolate with a small palette knife until it runs over the end of the strip. Spread out the chocolate in a thin and even layer. Place the strip in one clean side of the work surface and allow to set slightly until the strip is pliable and not fully set (about 5 minutes). Mark approximately 0.5 cm length on either end so the ends of the band are neat. Wrap the chocolate band around the cake with the chocolate side touching the mousse. Once the chocolate is completely set, peel back the acetate strip.
3. Make the 3 Ruby chocolate thin rings: grease slightly the work surface with a non-stick spray or a bit of butter and stick an acetate strip of 60 cm length and 3 cm high. Pour a line of tempered Ruby chocolate lengthwise and smooth the surface of the chocolate with a small palette knife until it runs over the end of the strip. Spread out the chocolate in a thin and even layer, then place the strip in one clean side of the work surface.
4. Make some thin strips by using a medium Benriner mandolin blade of 0,3 mm thick. Allow to set slightly until the chocolate is set to touch but pliable (about 5 minutes). Wrap the acetate strip around a 16 cm stainless steel cake ring (with the chocolate side touching the ring). Stick the two ends of the acetate strip with a piece of tape and set to room temperature (or if your room temperature is too warm place the strip in the fridge) for a short period to set.
5. Remove carefully the ring, cut the tape and peel back gently the acetate strip to release the Ruby chocolate rings.
6. Place 3 Ruby chocolate rings on top of the cake and finish the decoration with the edible flowers.