Preheat the oven to 160 C fan and line a 12-hole muffin tray with 12 large cupcake cases.
Cream the margarine on a high speed in a mixer for 2-3 minutes until lighter in colour and fluffy in texture.
230 g margarine
Add the sugar and whisk again on a high speed until fully incorporated.
230 g caster sugar
Whisk in the eggs one at a time and then the bourbon vanilla extract.
4 large eggs, ½ tsp Bourbon vanilla extract
Sift in the flour, salt, baking powder and Xanthan Gum, and mix in on a low-medium speed until just incorporated and no pockets of flour remain.
230 g gluten-free self-raising flour blend, ¼ tsp salt, ½ tsp baking powder, ¼ tsp Xanthan Gum
Use an ice cream scoop to spoon one generous scoop into each of the cupcake cases, dividing the mixture evenly.
Bake on the middle shelf for around 20-25 minutes, until springy to the touch and an inserted toothpick comes out clean with no wet crumbs stuck to it.
Allow the cupcakes to cool for a minute or two, before transfering to a cooling rack to cool completely before preparing the buttercream.