Chocolate & Orange Cake

Ok, there is a tiny problem of how long it takes to bake. I don't know if it is my oven or something else. If it isn't cooked by in the time it says it should, just put it in for another 5 - 10 minutes, then use a skewer to check. It usually take me about 35 to 40mins.

175gm Caster sugar
175gm Butter
3 Eggs, beaten
175gm Self raising flour, sieved
2 Tbsp cocoa powder, sieved
2 Tbsp milk
3 Tbsp orange juice
grated rind of 1/2 orange

Icing (optional, cos some people say it's too sweet)
175gm icing sugar
2 Tbsp orange juice

Steps

1. Lightly grease 20cm round cake tin, line if you like. Preheat oven (190C/375F/Gasmark 5).
2. Beat together sugar & butter until light & fluffy. Gradually add eggs (about 3 times), beating well after each addition. Carefully fold in the flour.
3. Divide mixture in half. Add cocoa powder and milk into one half, stirring till well-combined. Do the same with the other half, with the orange juice and rind.
4. Place spoonfuls of each mixture into cake tin and swirl with skewer or butter kniffe for marbled effect.
5. Bake in oven for 25 mins or till springy to touch.
6. Leave to cool in tin before transfering to wire rack.
7. For icing, sift icing in mixing bowl and mix orange juice to form smooth icing. Spread icing over the top of the cake and leave to set before serving.

Variation:
2 Tbsp of rum/brandy to chocolate instead of milk if you like to be a little drunk. Lemon also works well instead of orange. (this is what the book says, but i still prefer the choc, milk and orange)