Line a 20cm square cake tin with baking paper and preheat your oven to 180 degrees.
Sift the self raising flour, bicarb soda and cocoa together into a small bowl and set aside until needed.
Place the softened butter and both of the sugars into your electric mixer bowl and beat until the mixture turns pale and is light and fluffy.
Add the eggs one at a time and beat well between each addition.
Add the vanilla extract and jam and beat until well combined.
Add the sifted flour mixture and the milk alternatively to your mixing bow - keep it beating on a low speed. Once all of the ingredients have been added, continue to mix for a further 30 seconds or until all the ingredients have combined.
Pour the cake batter into the prepared cake tin and place in the oven to bake for 40 minutes or until cooked through when tested with a skewer.
Carefully remove the cooked cake from the oven and allow to cool in the tin for approximately 20 minutes before carefully turning out onto a wire rack to cool completely.
Once your cake has completely cooled, you can then make the chocolate buttercream.
Place all of the ingredients for the Chocolate Buttercream into a small saucepan and stir over a low heat until the ingredients have all combined and the icing is smooth and glossy.
Spread the buttercream over the top of the cooled cake using a spatula or butter knife.