Line a muffin tin with either small or large cases and grease them with a little melted butter.
Gently melt the remaining butter with the lemon zest to release the oils.
Whisk the eggs with the cooled melted butter and the rest of the ingredients and leave to cool.
Poor the mixture into the muffin cases and bake for 10-20 mins depending on size – they are ready when they are still a little wet inside as they will continue to cook.