• Preheat the oven to 180'C (170'C fan) / Gas 4. Fill a 12-hole baking tin with cupcake cases and set aside while you make the cake batter.
• Add the butter and sugar to a large mixing bowl and beat with an electric whisk until pale and creamy. (TIP: If the butter is hard, zap it in the microwave for 10-15 seconds before adding it to the mixing bowl to make it easier!)
• Crack the eggs into the mixing bowl and add the lemon zest. Beat again for 30 seconds to combine. Scrape down the sides of the bowl using a spatula.
• Sift in the self-raising gluten free flour and xantham gum, add the milk, and then beat together with the electric whisk until everything is fully combined. You want a fairly thick batter which looks light and fluffy.
• Spoon the mixture evenly between the cupcake cases and then place in the centre of an oven and bake for 20-22 minutes. The cupcakes are done when they are well-risen, golden on top, and a skewer inserted in the middle comes out clean.
• Once cooked, remove from the oven and place on a cooling rack. Add the caster sugar and lemon juice for the drizzle into a saucepan and heat, stirring until the sugar has dissolved. Spoon evenly over the warm cupcakes. Cool the cakes in the tray for 10 minutes before removing the cakes from the tray to cool completely.

To make the frosting:

• Add the butter, icing sugar and 2 tbsp lemon juice to a large mixing bowl and beat with an electric whisk on a low speed until it becomes a smooth, pale buttercream. (TIP: To avoid an icing-sugar dust cloud I tend to 'mash' the mixture with a fork until it starts to come together, then use the electric whisk).
• If the mixture is too thick, add a little extra lemon juice at a time - you should need no more than 3 tbsp which is approx one large lemon. To make marbled icing, spoon half of the icing into a separate bowl and mix with yellow food colouring. When adding to the piping bag, spoon the frosting in, alternating between the yellow and white icing.
• Once the cupcakes are completely cool, decorate them with a swirl of buttercream. Finish with some extra lemon zest.