Pre-heat oven on gas mark 5. Line a muffin tin with muffin cases. Sieve the flour, baking powder, bicarbonate of soda, caster sugar into a bowl and mix together. Make a well in the dry ingredients.
Add the lemon juice, extract and eggs into a jug then add enough yogurt until you have about 300ml of liquid then mix together. Add the melted butter and wet ingredients and add them to the dry ingredients.
Using a spatula to mix all the ingredients together until combined, once combined stop mixing so that the mixture is not over worked.
Then fill each case about three quarters full then add about a teaspoon of lemon curd to each cupcake.
Then add a little bit more mixture to cover the lemon curd. Put them in the oven for 20 minutes.
Once the muffins are cooked, leave them in the tray for about 5 minutes to cool then move them to the cooking rack.
Add a little bit of lemon juice to the icing sugar until you have a thick but runny consistency. Then add a spoonful to the top of each muffin once they have cooled a little.