Preheat the oven to 200C.Line a 12-hole deep muffin tin with paper cases.Melt the butter in a small pan over a low heat then set aside to cool for a few minutes.Sift the flour and bicarbonate of soda into a large bowl and stir in the sugar,blueberries and lemon zest. make a well in the center.
Beat the eggs well with a fork until smooth then beat in the yogurt, milk and meltedbutter until well combined. Stir into the flour mixture with a large metal spoon until very lightly mixed.Divide the batter between the muffin cases. Bake for 20 minutes or until well risen and golden- brown. Serve warm or allow to cool on a wire rack.