- In a bowl, beat the eggs and sugar with an electric mixer for 5 minutes.
- Add the citrus zest and blend.
- With a spatula, gently fold the flour and butter into the egg mixture.
- Let the batter rest in the refrigerator for 1 hour.
- With the rack in the middle position, preheat the oven to 190 °C (375 °F).
- Generously butter and flour madeleine molds. Fill each mold up three-quarters. Bake for about 14 minutes or until lightly browned.
- Unmould immediately out of the oven.
- Store the cooled madeleines in an airtight container.