Heat oven to 190C/fan 170C/gas 5. Butter two 20cm sandwich tins and line with non-stick baking paper.
Divide the mixture between the tins, smooth the surface with a spatula or the back of a spoon.
Bake for about 20 mins until golden and the cake springs back when pressed.
Turn onto a cooling rack and leave to cool completely.
To make the filling, beat the 100g softened butter until smooth and creamy, then gradually beat in 140g sifted icing sugar and a drop of vanilla extract (if you’re using it).
Spread the buttercream over the bottom of one of the sponges. Top it with 170g strawberry jam and sandwich the second sponge on top.
Dust with a little icing sugar before serving. Keep in an airtight container and eat within 2 days.