Chocolate Custard Cake Box

Beat the softened butter with powdered sugar until smooth.

Add the egg and mix well.

Fold in the flour, cocoa powder, and salt.

Knead just until the dough comes together.

Immediately roll out into a thin layer between two sheets of parchment paper.

Bake at 170°C for about 12–15 minutes until done.

Let cool completely and break into pieces.

Whisk together the egg yolks, sugar, and starch.

Bring the milk to a near boil.

Temper the yolks by pouring in a portion of the hot milk while whisking.

Return the mixture to the saucepan and cook until thickened.

Remove from heat, then stir in the butter and vanilla paste.

Cover with plastic wrap directly on the surface and chill completely.

Whisk the chilled custard base until smooth.

Whip the cold heavy cream to soft peaks.