Preheat oven to 350F / 180C. Grease and line 2 x 8”/20cm round cake pans.
Beat the butter and sugar in a large bowl until combined and pale. Add all the remaining cake ingredients and beat well.
Divide the batter evenly between the cake pans and spread to the edges. Place in the oven and bake for 25 minutes or until an inserted toothpick or skewer comes out clean.
Allow the cakes to cool in the pans for 10 minutes, then turn out onto a wire rack to cool completely.
For the frosting
Beat the ingredients together until fluffy. If it's too runny, add a little more icing sugar. If it's too thick, add a little milk, a tablespoon at a time.
When the cake is completely cooled, frost the top of the bottom layer, add the top layer and spread the frosting around the top and sides. Decorate with orange zest.
Turn this into choc orange cupcakes by filling the 12 cups of a lined muffin pan and bake for 15-20 mins.
Increase the ingredients by an extra 50% for a three layer cake.
The frosted cake is best stored on the kitchen counter for up to 5 days. You don’t need to tightly wrap it, but a cake tin will ensure the cut edges don’t dry out and keep it clean.
If the weather is very warm, you can keep the cake in the fridge. Put it into an airtight container or wrap it. Let the cake warm up to room temperature before eating.
You can store un-frosted cake layers, well wrapped, on the kitchen counter for up to 6 days. If you need to keep them longer than that, then it's best to freeze them.
This chocolate orange cake is freezable: you can freeze the un-frosted cake layers for up to 1 month. Wrap each completely cooled layer well in plastic wrap and freeze them. Then let them defrost and add your favorite frosting.
If you've already frosted the cake, you can still freeze it. Wrap it a little looser, then freeze. Allow to thaw and enjoy.