1. Heat the oven to 350ºF/180ºC. Beat the yogurt and the sugar together in a bowl. Beat in the eggs and lemon zest. Sift the flour with the baking powder and beat inches 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, approximately 25 minutes.
2. Note: recipe makes 12 muffin-sized cakes, or 1 loaf.