Preheat the oven to 170°C (338°F). Grease the 20 cm round cake pan with 10 g margarine and dust it lightly with wheat flour.

Sift 185 g wheat flour, 40 g cocoa powder, 20 g milk powder, and 4 g baking powder into a mixing bowl. Whisk or stir the dry mixture until evenly combined.

Beat 300 g butter and 200 g icing sugar at high speed until pale, fluffy, and increased in volume. Scrape down the bowl as needed.

Add the 5 eggs one at a time. Beat each egg for 1 minute at low speed before adding the next egg.

Fold the dry mixture into the butter mixture in batches until no dry flour remains. Use gentle spatula strokes to keep the batter airy.

Add 65 ml chocolate sweetened condensed milk and 5 ml dark chocolate paste. Fold until the batter is smooth and evenly chocolate-colored.

Pour the batter into the prepared 20 cm cake pan. Smooth the top with a rubber spatula.

Bake at 170°C (338°F) for 50 minutes, or until a skewer inserted in the center comes out clean. Cool the cake in the pan for 10 minutes.

Remove the cake from the pan and transfer it to a cooling rack. Cool completely before slicing into 10 portions.