Cream together the margarine, butter and caster sugar on a medium speed for around 3 minutes. Scrape around the sides of the bowl and then mix again briefly.
Crack eggs into a bowl or jug and add 1 teaspoon of vanilla bean paste. Then start adding the eggs in slowly on a slow to medium speed into the butter/sugar mix.
Add in self raising flour with a ¼ teaspoon of salt added to the flour. Fold in by hand and then add in buttermilk and fold in further. You can also mix on a low speed on your stand mixer for around 30 seconds. Be careful not to overmix.
Split the cake batter between two 7 inch cake pans and bake in a pre heated oven at 160 degrees for around 25 minutes or until a skewer or knife comes out clean.
Cool completely and fill with buttercream and jam.
To make the buttermilk, add 45ml of full fat milk to a bowl and add 3ml of white vinegar or lemon juice from a fresh lemon. Let it rest for 15 minutes before use.
Mix the butter until light and fluffy. Add in your icing, vanilla and milk and further mix until it's all incorporated for around 2 minutes.
