Preheat the oven to 180°C / 160°C fan / gas mark 4. Grease and line two 20cm sandwich tins.
Cream the butter and sugar in a large bowl until pale and fluffy.
Add the eggs, one at a time, beating well after each addition. Stir in the vanilla extract.
Sift in the flour and baking powder, folding gently to combine. Add the milk to loosen the mixture slightly if needed.
Divide the mixture evenly between the two prepared tins and smooth the tops.
Bake for 25–30 minutes, or until golden and a skewer inserted into the centre comes out clean.
Cool in the tins for 5 minutes, then turn out onto a wire rack to cool completely.
Prepare the buttercream filling: Beat the butter, icing sugar, and vanilla extract until light and fluffy.
Assemble the cake: Spread buttercream over one sponge, top with raspberry jam, then place the second sponge on top.
Dust with icing sugar before serving.