Okay, I can take NO credit for this one. Nor has it needed to be adapted. It comes from a blog called ChickensInTheRoad, and I hope they don't mind me sharing it here.
I personally prefer from-scratch cake to from-the-box, even when I lived in the US. But somedays I really need to be able to whip something up without the hassle of pulling out all the ingredients and measuring (okay, so truth be told, most of the time I can't be bothered with proper measuring anyway). So to have a home-made mix that I keep in the pantry (okay, here, because of the bugs, in the freezer) ready to pull out at a moment's notice.
2 cups flour
1 1/2 cups sugar
1 Tbs baking powder
1/2 cup milk powder
When you're ready to make the cake:
3/4 cup water
1 tsp vanilla
1/2 cup butter
Blend all ingredients together with an electric mixer (although a wooden spoon works just as well when the power goes out) for 2 minutes. Pour into greased & floured (or lined-with-a-reusable-silacone-non-sticker-pad) cake pan and bake. You should know the rest.
8 or 9 inch round pan: 20-25 minutes
13x9 inch pan: 35-40 minutes
Cupcakes: 12-15 minutes
Bundt: 45-50 minutes