1) Make the sponge

1. Heat the oven to 180°C / 350°F. Grease and flour the pan (or use a silicone pan).
2. Separate egg whites and yolks. Mix flour with baking powder.
3. Whip the whites to soft peaks. When foamy, add sugar gradually and whip to a firm, glossy meringue.
4. Add yolks immediately, then add the flour mixture. Mix briefly—stop as soon as combined.
5. Pour into the pan and bake 16–20 minutes (fan ovens can be faster).
6. Unmold and cool on a rack. For best slicing, chill overnight and cut into 3 discs the next day.

2) Make the coffee syrup

1. Bring water and sugar to a boil for about 5 minutes.
2. Remove from heat, stir in instant coffee until dissolved, then cool completely.

3) Make the mascarpone mousse

1. Bloom gelatin in cold water for 15 minutes.
2. Separate whites and yolks. Whisk yolks + vanilla + 160 g sugar until pale.
3. Warm 50 ml of the cream (taken from the total). Remove from heat, dissolve the squeezed gelatin in it.
4. Loosen mascarpone, then mix it into the yolk mixture.
5. Add the warm (not hot) gelatin-cream mixture.
6. Whip the remaining cream to firm peaks and fold it in gently.
7. Whip the whites, then add the remaining sugar and whip to a stable meringue.
8. Fold whites into the mascarpone mixture until light and airy.
9. Use the bowl-weighing method to split mousse evenly into 3 portions.

Assemble the tiramisu layer cake

1. Place the cake ring on a serving plate and line the inside with an acetate strip.
2. Add the first sponge disc and soak generously with coffee syrup.
3. Spread 1/3 of the mousse and smooth.
4. Add the second disc, soak, then spread the second third of mousse.
5. Add the final disc, soak, then spread half of the remaining mousse on top.
6. Put the rest of the mousse in a piping bag and keep chilled.
7. Freeze the assembled cake for at least 3 hours (for a clean unmold).
8. Unmold quickly, remove acetate, pipe the border, then refrigerate.
9. Thaw in the fridge for at least 6 hours before serving.
10. Finish with cocoa powder right before serving.