Pre-heat oven to 180°C / 160°C fan assisted /gas mark 4 / 350°F and line a 12-hole muffin tin with cases.
Beat the butter and sugar together until light and fluffy. About 6 minutes in a stand mixer, scraping the sides down occasionally.
Add the eggs one at a time, beating well after each addition and then add the vanilla extract.
Whisk together the gluten-free flour, ground almonds, baking powder and salt.
Add the flour mixture to other ingredients and beat well.
Divide the batter between the muffin cases.
Bake for 20 minutes until the surface is just turning golden.
As soon as the tin has been taken out of the oven, then lift out the fairy cakes and leave on a cooling rack to cool completely before icing.
Make the icing by beating together the lemon juice and zest with the icing sugar until the icing is a thick paste.
Drop a teaspoon of icing on each fairy cake and use the back of a teaspoon to swirl around to the edges.
Decorate the fairy cakes with plenty of colourful sprinkles.