• Preheat the oven to 180'C / Fan 160'C / Gas Mark 4. Grease and line two 20cm (8 inches) round baking tins (see blog post above for details on how to line your tins). Mix the gluten free flour, baking powder and xanthan gum together in a bowl and set to one side.
• Add the caster sugar and Stork to a large mixing bowl and beat with an electric whisk for a minute until creamed together.
• Add the eggs and milk to the mixture and then sift in the flour mix. Beat again with the electric whisk until the mixture has combined to form a smooth batter.
• Divide the mixture evenly between the two cake tins and smooth out the tops. Bake in the oven for 30-35 minutes until golden on top and springy to the touch. A skewer inserted in the middle should come out clean. *Do NOT open the oven before 30 minutes and hold off until you know the cakes are done, otherwise they will sink!
• Remove the cakes from the oven and place on a cooling rack. Leave to stand until the tins are cool enough to remove, then remove the tins and leave the sponge to cool completely. (See notes if you're making the sponge ahead of time)

To assemble:

• To make your icing, add the butter, icing sugar, vanilla extract and milk to a large mixing bowl and beat together until it forms a smooth buttercream.
• Use a cake-leveller to flatten the bottom sponge, and then spread evenly with the jam. Turn the other sponge upside-down and spread the buttercream in a thick, even layer over the flat side. Sandwich the two sponges together with the cream and jam in the middle.
• Sprinkle liberally with icing sugar and serve straight away.