To make the sponge, add the granulated sugar and soften butter to a bowl, and beat well with a hand mixer until creamy.
Add the eggs and mix again, then add the flour, vanilla extract and baking podwer, and mix to get a smooth batter.
Butter and flour two cake tins (19 cm, 7.48 inches), and divide the batter evenly between the tins.
Bake in the preheated oven at 180 degrees Celsius (350 Fahreneheit) for 20 minutes, or until golden, and a skewer inserted in the middle comes out clean.
Leave the cakes to cool down.
To make the buttercream, sift the icing sugar with the butter, then add the vanilla extract and milk, and mix again to get a silky cream.
To assemble the cake, spread the icing over the bottom of one cake, spread the jam over, and top with the second cake.