Preheat oven to 170°C.
Cream together the butter and sugar. Add eggs one at a time. Add the finely grated ginger, blending until the mixture is smooth. Fold in the flour, mixing well with a spatula.
You could use a 22 cm baking tin and line with butter and baking paper. We like to serve this cake in a long loaf tin, but it works well this way too. Pour the mixture into the tin, then using a spatula, make a slight indentation on top of the cake batter. Pour the sour cream or Greek yoghurt into this indentation and sprinkle with the granulated sugar. Bake for 45–50 minutes until cooked.
When the cake comes out of the oven, sprinkle with a bit of extra organic sugar for a bit of crunch and sparkle.