Blend sugar and eggs in a large bowl. Add melted butter and blend well. Blend in flour, baking powder, lemon juice, lemon zest, and vanilla on low speed. Cover the bowl with a dish towel and let sit at room temperature for 1 hour.

Preheat the oven to 375 degrees F (190 degrees C). Butter and flour madeleine molds.

Whisk batter and spoon into the prepared molds, 3/4 full.

Bake in the preheated oven for 10 minutes. Remove madeleines from the molds to a wire rack to cool completely. Dust with confectioners' sugar.