Wash the lemon thoroughly and prepare the zest and juice.
Add eggs, erythritol, and salt to a bowl and whip together.
Sift cake flour and baking powder, then add and mix well.
Add lemon zest, lemon juice, and melted butter to complete the batter.
Brush butter on madeleine molds and fill with the batter.
Bake in a 170°C oven for 12–15 minutes.