Preheat the oven to 180ºc
Add the peanuts to a grinder and grind (don't worry if there are a few big pieces left)
Cream the butter and sugar until pale
Add one egg at a time and mix until smooth
Next add the flour, baking powder and bicarb and mix well until there are no lumps left
Fold in the crushed peanuts and transfer the batter into a greased cake tin
Bake at 180ºc for 20-40 min or until cake is golden brown