Heat oven to 190C/fan 170C/gas 5.
Assemble Wilton Countless Celebrations tin (instructions are provided) into your desired letter and spray the tin with vegetable oil.
Cream together 400g butter and 400g caster sugar until light and fluffy.
Add 4 eggs and 8 tablespoons of milk until you have a smooth batter.
Into the bowl, sieve 400g self-raising flour and 2 teaspoons of baking powder. Fold the mixture together using a wooden spoon.
At this point, you can do the 'drop test'. If the mixture falls easily from the wooden spoon and drops into the bowl the mixture is fine. If it sticks to the spoon - add more milk, a tablespoon at a time until you are at 'dropping' stage.
Pour the mixture into your prepared tin and bake in the oven for 30 minutes or until a skewer inserted into the middle of the cake comes out clean.
Once baked remove the cake from the oven and leave to cool inside the tin.
Once cool, turn the cake out onto a board and cut it through the middle using a serrated knife so that you have two cake layers. You can freeze them at this point or wrap them in greaseproof paper until it's time to decorate.
Spread strawberry jam (about 5 tablespoons) onto the first cake layer and top with buttercream icing (instructions to make buttercream below.) Sandwich the second layer on top of the first layer and repeat the jam and buttercream step.