Start preparing the dough. To do this, beat the eggs with sugar in a deep bowl with a mixer. Separately mix the flour and baking powder. Add the flour to the egg mixture and mix. Then pour in the melted butter and mix until smooth.
Prepare the lemon filling. Grate the zest of one lemon. Squeeze out the lemon juice. Add the juice and zest to the dough and mix.
Bake the muffins. Pour the batter into the muffin tins, filling them halfway. Bake for 25-30 minutes. Remove the muffins from the tins, cool, and serve. Enjoy!