Preheat the oven to 200C/400F/Gas 6. 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 centre.
Beat the eggs with a large whisk until smooth then beat in the yogurt, milk and melted butter until well combined. Stir into the flour mixture with a large metal spoon until very lightly mixed.
Divide the batter between the muffin cases. Place a teaspoon of the lemon curd on top of each one and sprinkle with the remaining sugar. Bake for 20 minutes or until well risen and golden-brown. Serve warm or allow to cool on a wire rack. (The lemon curd will be very hot, so don’t eat as soon as they come out of the oven.)