Rubik’s cake (Cédric Grolet)

To start 2018 off right, I set myself a small challenge, to create a Rubik's cake inspired by Cédric Grolet, but not just any: I based it on the recipe published by Fou de Pâtisserie to make my own Christmas Rubik's cake by adapting the flavors to those of my family. I made this cake for my grandmother's 80th birthday, and by organizing myself well, I managed to make this famous dessert emblematic of Le Meurice. Of course, it's better not to count the hours of preparation and to allow a lot of time for decoration, but by preparing the cubes a few days in advance and keeping them in the freezer, I only had to do the glazes on D-Day, so it was :-) Equipment-wise, I went to buy three 11cm plexiglass squares at a hardware store, and I prepared 3.6cm high chocolate tubes to hold the structure. Finally, I had prepared a small diagram to know where to place all the cubes as they were being prepared/decorated, it was simpler in terms of organization this way!

The fillings:

Lemon marmalade:

200g of lemon juice
20g of sugar
3g of agar-agar
120g of lemon zest
240g of water
240g of sugar
25g of fresh lemon segments

Boil the lemon juice. Separately, mix the sugar (20g) with the agar-agar, then pour the mixture into the lemon juice. Cook for 2 minutes, then pour into a dish and refrigerate.

Cut the lemon zest into pieces, then place them in a saucepan. Fill the saucepan with cold water, then bring to a boil. Drain the zest, then repeat the operation twice.

Next, prepare a syrup by boiling water with sugar. Dip the zest into it and cook on low heat (without bringing to a boil) for several hours (the lemon zest is thick, it needs quite a bit of time to candy). They are ready when the zest is very tender.
Drain the zest, then cut them into very small pieces. Also cut lemon supremes into small pieces.

Take the lemon jelly out of the refrigerator and blend it, then add the lemon zest and supremes. Keep refrigerated.

Mandarin marmalade:

200g of mandarin juice
20g of sugar
3g of agar-agar
120g of mandarin zest
240g of water
240g of sugar
25g of fresh mandarin segments

The process is exactly the same as for the lemon marmalade, except the zest cooks faster.

Pistachio praline:

100g of pistachio
50g of granulated sugar
1g of fleur de sel
15g of water

Roast the pistachios for 20 minutes in an oven preheated to 150°C.
Then prepare a caramel with water and sugar (the caramel is ready when it has a nice amber color) then pour it over the roasted pistachios.

Add sea salt, then when the mixture has cooled, blend it until smooth.

Prepare the following two fillings only when the cake is baked and cooled, the assembly will be easier if they haven't had time to harden.

Guanaja ganache:

57g of Guanaja chocolate (or chocolate of your choice)
12g of invert sugar
70g of heavy cream

Melt the chocolate. Separately, boil the heavy cream and invert sugar. Then pour the cream in three times over the chocolate, stirring well to achieve a smooth and shiny ganache.

Chocolate-hazelnut praline crunch:

80g of hazelnut praline
32g of dark chocolate

Melt the chocolate, then add the hazelnut praline, stirring well.

The cake:

Vanilla cake:

125g of eggs
40g of trimoline (or invert sugar)
60g of sugar
40g of almond powder
75g of T45 flour
4g of baking powder
65g of heavy cream
40g of grape seed oil
25g of Ivoire chocolate
1 vanilla bean

Beat the eggs with sugar, trimoline, and vanilla. Add the almond powder, baking powder, and flour mixture then the heavy cream.

Melt the chocolate, then add the grape seed oil.
Mix part of the cake batter with white chocolate, then put the mixture back into the rest of the batter.

Pour the batter onto a baking sheet, then bake at 180°C for 8 minutes.

Assembly:

Cut the cake into small squares using cube-shaped molds (be careful, the quantity of cake is quite tight and you still need 50 squares).
Prepare five rows of 5 cubes and place a cake square at the bottom of each cube.
In the first row, add lemon marmalade.
In the second, add mandarin marmalade.
In the third, add pistachio praline.
In the fourth, add chocolate ganache.
Finally, in the last, add the chocolate-hazelnut praline mix.
Finally, close each cube with a cake square, then place it all in the freezer.

When all the cubes are frozen, unmold them and keep them in the freezer while preparing the glazes.

Glaze and decoration:

Here are the decorations I chose for the different flavors:
- Lemon cubes: white velvet glaze
- Mandarin cubes: white mirror glaze
- Pistachio cubes: white chocolate pistachio rock glaze
- Chocolate cubes: silver leaf
- Chocolate-hazelnut cubes: hazelnut powder

You can of course adapt the decorations according to your tastes and chosen flavors.

Start by preparing the white coating:

200g of Ivoire white chocolate
200g of cocoa butter
4g of titanium dioxide

Heat the cocoa butter, then pour it over the Ivoire chocolate. Add the white coloring, then blend everything using an immersion blender.

When the glaze is at 32°C, dip the lemon, mandarin, pistachio, and chocolate cubes into it, then place them back in the freezer.

Then dip the choco-hazelnut cubes into it, then sprinkle them with hazelnut powder before the glaze has time to harden. I advise placing the cubes on plexiglass plates as soon as their decoration is done, using a pre-made diagram.

Next, take the lemon cubes out of the freezer and spray them with the white velvet glaze.
Cover the chocolate cubes with silver leaf.

Then prepare the mirror glaze:

140g of milk
290g of heavy cream
280g of sugar 1
100g of glucose
10g of titanium dioxide
25g of starch
90g of sugar 2
10g of powdered gelatin
60g of water for the gelatin

This quantity of glaze is very large, I think it's suitable if you want to use this glaze for the 25 cubes. Since I'm only using it for 10 cubes, I think halving this quantity should suffice.

Hydrate the gelatin in cold water.
Bring the milk, cream, sugar 1, and glucose to a boil. Then add the titanium dioxide mix, sugar 2, and starch, whisking well, and bring to a boil while continuing to stir.
When the glaze is at 40°C, incorporate the gelatin, then blend using an immersion blender and strain through a chinois.

Divide the mixture in two, and in one of the glazes add the crushed pistachios.

Finally, dip the mandarin cubes in the smooth glaze, and the pistachio cubes in the rock glaze, then place them on the Plexiglas plates.

Stack the three plates by placing your chocolate tubes in the center of the two bottom plates, then let the cubes thaw and enjoy, you've earned it ;-)