Lemon & orange cake

This citrus centrepiece has a secret ingredient that gives the cake a lovely texture, yet makes it gluten- and wheat-free

250g pack butter, softened
250g golden caster sugar
4 eggs
250g gluten-free self-raising flour (we used Doves Farm, which is also wheat-free)
2 tsp gluten-free baking powder
250g mashed potatoes, forked through so it doesn't go in as one lump
2 lemons, zest and juice
1 orange, zest and juice
175g icing sugar
squeeze lemon juice (save a little from the cake quantity)
chocolate eggs, to decorate, if you like (check they're gluten-free)

Heat oven to 180C/160C fan/gas 4. Grease and line a deep, 20cm round cake tin. Beat the butter and sugar together until pale and fluffy, then gradually beat in the eggs, one by one. Fold in the flour, baking powder, mashed potato, zests and juices. Scrape into the tin and level the top. Bake for 45 mins until golden and a skewer poked in comes out clean. Cool in the tin for 10 mins, then move to a wire rack.
Sift the icing sugar, then mix in enough of the lemon juice to make a stiff, but still runny icing. Spread over the cake so it dribbles down the sides a little. Add some chocolate eggs, if using. Leave until the icing has set, then slice and serve. Delicious with a dollop of natural yogurt.