First, prepare the pastry cream filling. Crack the eggs and weigh them, since you’ll need the same weight in sugar for this step.

Dissolve the cornstarch in a little of the measured water, then mix it in a bowl with the eggs and the rest of the water. Make sure there are no lumps. Finally, add the sugar to the bowl and mix well.

Pour the mixture into a saucepan and cook over low heat, stirring constantly until it thickens to a creamy consistency. Remove from heat and transfer to a piping bag.

While the cream cools, prepare the syrup. This is very simple: just put the water and sugar (equal amounts) in a saucepan. Bring to a boil and let it boil for 5 minutes. Remove from heat and set aside.

Now for the sponge cake. It’s super soft and delicate. Separate the egg whites from the yolks. Beat the egg whites with the sugar until stiff peaks form. Set aside. In another bowl, beat the yolks with the sugar, then add the milk, sifted flour, and cornstarch, and keep beating until smooth and lump-free.

Gently fold the beaten egg whites into this mixture using slow, folding motions.

Prepare a rectangular baking sheet. Grease it lightly with butter so the parchment paper sticks well. Pour the batter onto the sheet and smooth it out with a spatula so the surface is even and fully covered.

Bake in a preheated oven at 350°F (180°C), with heat from top and bottom, for about 10 minutes or until the edges start to turn golden.

Remove from the oven and place on a wire rack. Before it cools completely, turn it out onto a sheet of parchment paper and trim the edges to make a neat rectangle.

Using a pastry brush, coat the entire surface with the syrup.

Spread a thin layer of the reserved pastry cream over the cake. Leave about a 1/2-inch (1 cm) border without cream along one of the long edges. Sprinkle ground cinnamon to taste.

Roll up the cake and, using a sharp knife, cut it into 6 pieces. Stand them upright and top each with more cream from the piping bag. Sprinkle with sugar and caramelize the tops with a kitchen torch.

Keep refrigerated until ready to serve.