Preheat oven to 180 degrees Celsius. Prepare a loaf tin by lining with baking paper or spray with oil.
Mix yoghurt and sugar in a bowl with a wooden spoon until smooth.
Sift flour into bowl. Mix until it forms a smooth dough.
Pour dough into prepared tin. Bake for approximately 30 minutes until springy and lightly browned on top.
Turn out on a cooling rack to cool.
To make a marble cake: After step 3, divide dough into two bowls. Add 2 Tbs of cocoa and 1/2 Tbs plant based milk to one bowl. Mix until fully combined. Drop alternate spoonfuls of each mix into the prepared tin. Cut through several times with a knife to swirl the flavours. Smooth the top. Follow the baking instructions from step 4.