Preheat the oven to 160°C. Melt the butter and let it cool down. Chop the lemon zest.
In a bowl, whisk the eggs with the sugar until you have a homogenous dough. Pour the melted butter and the lemon zests and mix it all.
Let the preparation rest for 30 minutes.
Fill 2/3 of the Proflex mold and cook during 10 minutes. The madeleines should be golden and puffed. Unmold them warm.