Place the lemon in a pot with water.
Cook it for 20 minutes.
Preheat your oven to 190°C.
Whisk eggs and granulated sugar until pale and frothy.
Drain the lemons and remove any seeds.
Blend the entire fruit (peel and pulp) into a smooth puree.
Mix the milk, oil, vanilla, and lemon puree into the eggs.
Sift flour, baking powder, baking soda, and salt into the bowl.
Fold the mixture with a spatula until just combined.
Fill muffin liners ¾ full.
Bake for 18–22 minutes.
Cool the muffins completely on a wire rack.