Pre-heat the oven to 170℃ (338℉).
Prepare a muffin tin by greasing or lining with paper cases.
Beat the butter and sugar together until nice and fluffy.
Add the egg and vanilla and beat for a couple of minutes (until the mixture changes from dark to paler yellow).
Combine the flour, baking powder and baking soda and then stir in to the wet ingredients.
Finally, add the lemon juice and mix in.
Divide between six cupcake cases to half way full (they rise a lot).
Remove two tablespoons of berry sauce and set to one side.
With the remaining sauce, dollop around one teaspoon on the top of each cupcake and using a knife or skewer, gently swirl it in a little.
Bake for around 16-18 minutes in the lower part of the oven. The cakes are ready when an inserted skewer comes out clean. Allow the cakes to cool completely before frosting.