Frozen Strawberry Sacher Cake and Mousse

Preparation and base

Make the sponge base and set it aside for assembly.

1. Preheat the oven to 175 ºC at least 30 minutes before baking.
2. Melt the chocolate in a bain-marie, making sure that not a single drop of water gets into it.
3. In a bowl, mix the softened butter with the icing sugar using whisks, until you obtain a very creamy texture.
4. Separate the yolks from the whites and set them aside separately, making sure that no trace of yolk remains in the whites.
5. Add the yolks to the butter one at a time, stirring with the whisks, and do not add another until the previous one is fully incorporated.
6. Add the melted chocolate to the bowl with the eggs and butter, and stir until you obtain a smooth, shiny cream.
7. Transfer the mixture to a large bowl and set aside.
8. Whip the whites at medium speed until foamy.
9. Gradually add the sugar and continue whipping until you obtain a firm meringue, but not excessively stiff.
10. Fold 1/4 of the meringue into the bowl of chocolate and stir to incorporate it well.
11. Set aside the remaining 3/4 of the meringue.
12. Gradually incorporate the sifted flour and leavening agent into the chocolate, stirring gently with a spatula from bottom to top and from the center toward the edges while turning the bowl.
13. Once all the flour is incorporated, fold in the remaining meringue.
14. Add the rest of the whipped whites patiently and little by little, stirring gently with a spatula from bottom to top and from the center toward the edges while turning the bowl.
15. Place baking paper on a flat baking tray and spread the batter over it in a layer about 2 cm thick.
16. Bake at 180 ºC for 17-18 minutes.
17. Let it cool on a rack.
18. Mark the sponge base twice with the mold and cut out two pieces.
19. If using a round springform pan, cut the cake in half: first mark the cutting line with a knife and then cut it with fishing line, making a loop.
20. If using a round springform pan, once unmolded, wash it to use later as the container for assembling and freezing the cake.

Chocolate mousse

1. Hydrate the gelatin in very cold water.
2. In a bowl, mix the yolks with the sugar using hand whisks.
3. Bring the milk to a boil in a saucepan.
4. Pour the milk into the bowl of yolks and stir thoroughly.
5. Return the mixture to the saucepan and cook over low heat until it reaches 82 ºC, stirring constantly.
6. Remove from the heat, add the previously hydrated and well-drained gelatin, and stir until dissolved.
7. Melt the chocolate in a bain-marie, making sure that not a single drop of water gets into it.
8. Transfer the chocolate to a bowl.
9. Add the cream to the chocolate and stir.
10. Homogenize the chocolate with an immersion blender: place it switched off in the saucepan of chocolate, with the blades touching the bottom; switch it on without lifting it from the bottom or moving it, then switch it off and remove it.
11. Whip the cream to soft peaks.
12. Add 1/2 of the cream to the chocolate and stir slowly and gently with a spatula, from the center toward the edges, using folding motions.
13. Finish adding the other half of the cream and mix slowly.
14. Transfer the mousse to a piping bag.

Assembly, part 1 of the cake

1. Place the mold on baking paper, with a sturdy base underneath so it can be moved to the freezer.
2. If using a round springform pan, also place baking paper on the bottom of the pan and an acetate strip around the side wall.
3. If using a round springform pan, place one half of the cake on the bottom as a base, trimming it slightly if necessary so it fits.
4. Place a sponge base on the bottom, as the cake base.
5. Fill it with a one-centimeter layer of chocolate mousse and move the mold slightly to spread it evenly.
6. Set aside the remaining mousse.
7. Put the mold in the freezer so that the mousse firms up slightly.

Strawberry jam

1. In a small bowl, mix the sugar and pectin.
2. In a saucepan, heat the strawberry purée until it reaches 40 ºC.
3. Add the sugar and pectin mixture to the saucepan and stir vigorously.
4. Bring it to a boil over low heat and cook for 1 minute, stirring.
5. Remove from the heat and let it cool for 5 minutes, stirring constantly.

Assembly, part 2 of the cake

1. Remove the mold from the freezer.
2. Before the strawberry jam thickens, spread a thin layer of it over the semi-frozen mousse.
3. Place the other sponge base that you cut on top.
4. Put the mold in the refrigerator for 5-10 minutes.
5. Finish filling the mold with the chocolate mousse, without reaching the very top: leave a space of about 3 mm for the final shiny glaze.
6. Put the mold in the freezer for a minimum of 4-5 hours.

Final shiny glaze

1. Hydrate the gelatin sheets in very cold water a while beforehand.
2. Heat the cream, water and sugar in a tall pot until it comes to a boil.
3. Add the cocoa powder and cook until it reaches 103 ºC (63 Brix), stirring constantly with whisks, for about 10 minutes.
4. Transfer the glaze to a glass bowl and let it cool to 60 ºC.
5. When the temperature drops to 60 ºC, add the hydrated and well-drained gelatin, and dissolve it well by stirring with hand whisks.
6. Homogenize the glaze with an immersion blender: place it switched off in the saucepan, with the blades touching the bottom; switch it on without lifting it from the bottom or moving it, then switch it off and remove it.
7. Stir the glaze very slowly with a hand spatula to release any remaining air bubbles.
8. Let it cool to 35 ºC.

Final cake assembly

1. When the glaze reaches 35 ºC, remove the mold from the freezer.
2. Pour the shiny glaze over the mold and remove the excess by passing a spatula or the blunt side of a long knife over it.
3. Put it in the refrigerator for 5 minutes.
4. Carefully remove the mold.
5. Cut a 0.5 cm slice from each side with a very sharp knife so that they are clean and the different layers are visible.
6. Finish by decorating it with fresh strawberries on top and, if you wish, some thin pieces of tempered chocolate.
7. Let the cake thaw in the refrigerator.
8. If using the round springform pan, since the cake will be taller, pour in the glaze carefully and tilt the mold to spread it; once cold and unmolded, smooth the cake's edges.