You can tell by the splatter marks on this page what an essential recipe this for my family. This is from my cookbook We Love Food and the recipe is by my mother. Most cakes start here.
Here are my variations on a theme.
I do swap out: plain flour for SR flour and use 2 vanilla bean pods instead of extract that my mum uses
For chocolate cake, I add 2 cups of cocoa or 200 g of melted dark chocolate
For lemon and coconut cake, I add the rind and juice of 2 lemons, 1 cup of desicated coconut and 1 cup of greek yoghurt to keep it moist. I double this recipe and make 2 cakes, as my kids and friends are like vultures and the first one is eaten straight out the oven, so I need another one for afternoon tea/lunchboxes.
For apple crumble cake, I mix 1 cup rolled oats, 1/2 cup brown sugar, 1-2 chopped apples, 100 g melted butter in a bowl to make crumble mixture and sprinkle on top of cake batter before popping in the oven. Serve with double cream (or yoghurt).