I don't know what angel cake is but I'll give you a recipe for instant chocolate cake which you could make into a birthday cake.

Dry ingredients:

75g ground almond (almond flour)
75g dessicated coco nut
75g soy isolate powder (or soya flour, or increase the almond flour)
2 large dessert spoons of cocoa powder
1 heaped teaspoonful of baking soda
2 heaped dessert spoons powdered sweetener (I used splenda)

Wet ingredients:
four medium eggs
40g melted butter
about two dessert spoons of cream (add more if mixture is too dry)

Mix all the wet ingredients
add the dry ingredients and mix until it's a thick paste
turn it into a plastic sandwich box or other container and nuke it for about two and a half minutes. If it's wet give it another minute.

I made about six small cakes with the above mix. There is no reason you shouldn't make one big one.

You could cut it in half and add cream and dibetic jam (USA jelly) or dribble melted s/f chocolate over it.

The whole thing is about 7g carbs (or less) per 100g mix.