Beat soft butter, powdered sugar, vanilla and salt for about 5 minutes until fluffy and creamy.
Add eggs one at a time and beat briefly each time until homogeneous.
Mix 400 g flour with cocoa powder and baking powder.
Add the flour mixture to the butter mixture and mix briefly.
Now add the remaining flour little by little as needed and knead briefly to form a very soft chocolate dough.
Divide the dough into two equal pieces and refrigerate them, wrapped in an airtight container, for about 1 hour.
First roll one piece of dough slightly in flour, roll it out on a sheet of baking paper about 4 mm thick to a long rectangle or oval and cut out a number from it using the template.
Place the number together with the baking paper on which it was rolled out on a baking sheet and bake it in a preheated oven at 356 °F (180 °C) for about 10 minutes.
Roll out the resulting dough scraps in the same way on a sheet of baking paper, cut out the same number from it and bake it as the first one.
Now roll out the second piece of dough and cut out another number from it. Roll out the remaining dough and cut out the same number again.
Bake the last two numbers one after the other in the same way as the first.
Let the four cake layers in the shape of two equal numbers each cool.
Use the leftover dough to bake chocolate cookies.