Spread out the puff pastry dough on a baking sheet lined with parchment paper, poke it a bit with a fork, sprinkle on the sugar evenly, and bake golden brown for 30 minutes at 160 °C with the fan on. Turn over the dough and bake until the other side likewise turns a golden brown colour. Remove the dough and turn oven heat up to 220 °C. Sprinkle the dough with icing sugar and bake again until the sugar has caramelized. Then allow it to cool.

For the cream filling, heat the milk along with the cream, sugar, and vanilla pulp. Mix the egg yolks and the cornflour, at first stirring in just a dash of the hot milk-cream mixture and then continuing with the rest. Simmer until the mixture takes on a pudding-like consistency. Then stir until cool, working in cubed butter and adding the rum. Refrigerate for about 2 hours.

Use a serrated knife to cut the dough into 11 x 4 cm pieces. For each serving, first take one piece with its caramelized side face-down and use a piping bag to apply the cream filling in an even layer 1 cm thick. Then cover with a second piece. Repeat this process and top off with another piece of pastry. Set aside and decorate with mascarpone cream.