Red velvet cake

This cake is really popular at the moment it's a American recipe. The sponge is bright red it's a shame I didn't take a photo of the inside!
The topping is made of creme cheese and icing sugar it's surprisingly light. I used a Nigella lawson recipe for this the recipe was for cupcakes but I doubled the recipe and used a 10"inch round cake tin!
Ingredients ( needs to be doubled)
250g/ 8 oz plain flour
2 tbsp/ 30 mL cocoa powder
2 tsp/ 10 mL baking powder
½ tsp/ 2 mL baking soda
100g / 3 1/2 oz soft, unsalted butter
200g / 7 oz sugar
1 heaped tbsp/ 15 mL Christmas-red paste food colouring
2 tsp/ 10 mL vanilla essence
2 eggs
175 ml/ 3/4 cup buttermilk
1 tsp/ 5 mL cider vinegar

For the frosting (needs to be doubled again)500g/16 oz icing sugar
125g/ 4 oz cream cheese
125g/ 4 oz soft unsalted butter