Pre-heat your oven to 160C Fan/180C/350F/Gas Mark 4, and grease and line two 8" cake tins (that are at least 2" deep). I line the base with greaseproof paper and lightly grease the sides with butter
Make the sponge by mixing the butter/baking spread and caster sugar in a large bowl with an electric mixer, or in a stand mixer, for 3-4 minutes until fluffy. You can also mix by hand, but an electric mixer will give the best results
Add the eggs and vanilla extract, and whisk until fully incorporated, again using an electric mixer
Gently whisk in the self raising flour using a hand whisk, or fold in with a silicone spatula, and mix in until you can't see any flour anymore
Divide the mixture between the tins, use scales for accuracy if you like
Bake them for 20-25 minutes or until they are golden and a skewer inserted in the middle comes out clean. Leave them to fully cool either in the tins or remove from the tin and place on cooling racks
If the cakes have domed on top, you can level them off with a cake leveller or a knife, you will definitely need to do this for the bottom cake layer so that the top layer stacks on top of it nicely
To decorate the cake, prepare the double cream by whipping it along with the icing sugar and vanilla extract, with an electric whisk until soft peaks form. You can do this by hand but it will take much longer and require some muscles!
Put one of the sponges on your plate or cake stand and spread the jam onto it
Pipe or spread the whipped cream over the jam (or you can pipe or spread the cream on first and put the jam on top of it)
Add the other sponge on top and dust with icing sugar, or decorate how you like
Serve immediately, if using whipped cream store any leftovers in the fridge, if using jam only or jam and buttercream store in an airtight container in a cool place and eat within 2-3 days
Video
Notes
To make your own self raising flour, add 2 level teaspoons (a measuring teaspoon, not the kind you stir your coffee with) of baking powder to 200g plain flour or all purpose flour. Stir together well so the baking powder is evenly distributed throughout the flour.