Preheat the oven to 180˚C/ 160˚C fan/ gas mark 4. Put the Cupcake Cases in 12 muffin tins. Put the margarine in a mixing bowl with the caster sugar. Whisk together until creamy and light in texture and colour.
Gradually beat in the eggs and Vanilla Extract until well blended. Sift the flour and Baking Powder on top and using a large metal spoon, carefully fold the flour into the whisked ingredients.
Divide the mixture equally between the cupcake cases and smooth over the tops. Bake for about 20 minutes until risen, golden brown and just firm to the touch. Transfer to wire racks to cool completely.
Using a sharp knife, carefully cut a circle out of the top of each cake approx. 1cm away from the edge, scooping out a pocket of the cake sponge underneath at the same time. Trim away the excess sponge from each of the cake tops, to make a flat base.
Fill the centre of each cake with strawberry jam and pipe a generous blob of Buttercream. Place the sponge circle back on top of the buttercream and dust lightly with icing sugar. Your cakes are now ready to serve and enjoy!