for 7 cupcakes :
2 sp powder sugar,
2 sp cocoa powder,
2 sp yogurt ,
1 teacup of flour,
half teacup of water.
Mix margarine with sugar till gets white, add the egg, the cocoa, after teh yogurt and the flour and in the end water. Bake for 20 minutes at 200~
(you can always put stevia, 2% or 0% yogurt and low fat cocoa)
For the top :
1 spoon cherry marmelade (or the flavor you like), 3 spoon butter, 3spoons powdered sugar, mix well and put it when they are in room temperature.
for the peanut butter its the same but if youlove peanut butter maybe you can put equal quantity of peanut butter with margarine...