This recipe - whose attribution has been lost - is very easy to make and even easier to eat. Measurements were originally in US system but translate fine to metric.
Stir or sift flour and baking powder in a small bowl. In another bowl, stir cocoa into melted butter, then beat into mixture 1 cup sugar, 2 eggs and 3/4 teaspoon vanilla. Blend in dry ingredients. Spread half of batter in a greased 20 cm (8 inch) square pan.
In a bowl, Mix all cheesecake filling ingredients together (add a dash of milk if too thick). Pour mixture over chocolate batter in pan.
Spoon remaining chocolate batter over (again, add milk if it is too thick). Pull a knife through both batters to create a marbled effect.
Bake at 180 degrees C (350 degrees F) for 40 to 45 minutes. Cool, then cut into squares. Makes about 20.