Preheat the oven to 190įC (375įF, gas mark 5). Line a muffin tray with 10 paper muffin cases.
Place the sugar, butter, eggs, flour, baking powder and milk in a large bowl and mix with an electric whisk until pale and creamy.
Divide the mixture between the muffin cases and bake for 15-20 mins until risen, golden and firm to the touch. Transfer to a cooling rack. Leave to cool.
To make the buttercream, place the butter in a bowl and sift over the icing sugar. Beat until smooth.
Slice the tops off each cake and fill the cavities with a little buttercream and jam. Cut each sliced top in half and arrange on top of the filling to resemble butterfly wings. Dust lightly with icing sugar.