Preheat the oven to 200C/180C Fan/Gas 6. Line a 6 hole muffin tin.
In a large bowl, combine the dry ingredients (flour, baking powder, lemon zest sugar and a pinch of salt).
Make a well and add in the liquid ingredients (melted butter, milk, oil, lemon extract if using).
Stir together very gently with a wooden spoon, until only just combined. Scoop 1 tbsp of batter into each lined muffin hole, reserving about half the batter in the bowl.
Spoon 1 tsp of lemon curd on top of the batter for each muffin. Cover with remaining muffin batter.
Bake for 18-20 minutes, until golden on top. Let cool on a wire rack before making glaze.
Make glaze by combining icing sugar and lemon juice. It should be fairly stiff. Add more icing sugar/lemon juice to reach the consistency you like. Dollop onto each muffin, add a little lemon zest and serve!
