Preheat the oven to Gas Mark 4, 180°C, fan 160°C. Butter 2 x 20cm (8in) loose-bottomed cake tins and line with nonstick baking paper. Beat the Everyday Value butter and sugar with an electric hand whisk for about 5 minutes or until light and fluffy. Add the Everyday Value eggs, one at a time, and beat well after each addition. Then fold in the Everyday Value self-raising flour and baking powder using a large metal spoon. Fold in the Everyday Value milk and vanilla extract. Then divide the cake mix between the two tins and smooth the surface. Bake for 20 minutes or until a skewer inserted into the middle of the cake comes out clean and the surface of the cake is slightly springy to touch. Remove from the oven, leave to cool for 5 minutes in the tin and then turn out onto a wire rack. Leave to cool completely. For the filling, beat the Everyday Value butter until smooth and creamy using the electric hand whisk. Then gradually add the icing sugar and vanilla extract and beat until smooth. Spread the butter icing over one cake and then spread the Everyday Value jam on top of the icing - it works better than trying to spread it onto the other cake. Sandwich the cakes together and dust the top liberally with caster sugar.