In the bowl of a stand mixer fitted with a whisk attachment (a hand mixer works too), combine eggs, vanilla, & salt.
Whisk on high speed until pale in color.
Gradually, add sugar & continue to whip on high speed for 8 more mins. Batter is done when it holds a ribbon when the whisk is lifted.
Use a rubber spatula to fold the flour into the batter in thirds. Fold gently just until incorporated.
Add lemon zest and pour melted butter around the edges of the bowl so it doesn't deflate the batter.
Cover the bowl & chill the batter for 45 minutes and up to 4 hours.
Preheat oven to 375 degrees F. Remove the batter from the refrigerator & divide the batter evenly among a madeleine pan with 16 molds.
Bake for 12 minutes. Dust with sugar.