Preheat oven to 350 degrees F.
Coat madeleine pans with butter or baking spray. I used non-stick pan and baking spray.
Melt butter and allow to cool to room temperature.
Beat eggs and sugar together until light and fluffy, 3-5 minutes.
Add vanilla and lemon zest and beat for another minute.
Fill molds with batter until almost full. Use teaspoon or 1 1/2 diameter scoop.
Batter will be thick, so distribute evenly.
Bake for 10-12 minutes.
Cool for a few minutes and then invert and remove.
These are great served warm, but can be served at room temperature.
Cover with a cloth if serving that day.
You can also freeze.