Preheat oven at 180C.

Beat the butter with half the sugar until light and fluffy, then add the egg yolk one at a time, after each emulsifies.

Add the condensed milk, the flours and fold in.

Whip the egg whites and the remaining sugar until medium peaks.

Folk the flour mixture into the egg white mixture into three parts.

Divide the cake batter into 3 parts, and fold in the cocoa powder to one part.

Bake in three 7x7 inches baking tins.

When done, cool the cake and stack them up, using the strawberry jam to hold the layers together.