Heat the oven to 350ºF/180ºC.
Beat the yoghurt and the sugar together in a bowl.
Beat in the eggs and lemon zest. Sift the flour with the baking powder and beat in.
Finally, add the melted butter (or oil, although it doesn't taste quite as nice) and beat the whole mixture well.
Pour into non-stick muffin tins or a greased and floured loaf pan.
Bake until a toothpick comes out clean, about 25 minutes.
To make syrup-soaked cakes:
Heat orange or lemon juice with sugar, to taste, and cook until the sugar has dissolved, 3 to 5 minutes.
Prick the tops of the cakes with a fork, and spoon the syrup over so it sinks into the cakes.
Yield: About 12 muffin-sized cakes, or 1 loaf