First make the layers for the cake. Usually, puff pastry is sold in packets of 2 puff pastry sheets. Roll out each one carefully and cut it into 2. You have to get 2 rectangles from each puff pastry sheet - for a total of 4 layers.
Put each layer in an oven dish baking paper. Using a fork, make a bunch of holes in the puff pastry; the goal is to prevent it from rising too much. Bake each layer for 10 min. at 428°F (220 °C), they become ready very quick so keep an eye on them, bake to a golden color. Take them out and leave them to cool.
Even the layers out with a knife. If they're too puffy, scrape them down a bit and even off their edges. You can use the extra scraps at the end for decoration. Prepare the gelatin by putting it in a cup with 3 1/3 tbsp (50 ml) cold water and leaving it to swell.
Begin beating the yolks vigorously and slowly, in a thin trickle, start pouring in the milk, being careful not to curdle it. Once homogenized, return the pot to the stove and heat the cream until thickened for several min. The cream must not start to boil, so remove it from the stove before it does.
Put the swollen gelatin in the hot cream and stir so that it melts and is absorbed by the cream. Leave it to cool. Beat the confectionery cream into hard snow and pour it in lots to the other creamy mixture. Smear the cake well with cream on all sides and leave it to cool. Crumble the puff pastry scrapes and decorate the cake with them. If you have no puff pastry scrapes left over from earlier, you can decorate with fruits, walnuts or chocolate, as desired.
Leave the cake in the fridge for 12 hours to harden.