Delicately airy, buttery shells scented with fresh lemon zest, finished with a whisper of confectioners’ sugar for a crisp-edged, tender-crumb bite.
Melt 1/2 cup (113g) unsalted butter in a large bowl and set aside to cool slightly.
Using a handheld or stand mixer fitted with a whisk attachment, beat the eggs and granulated sugar together on high speed for at least 8 minutes until thick, pale, and forming ribbons. Beat in the lemon zest and vanilla extract until combined.
In a separate bowl, whisk together the flour, baking powder, and salt.
Using a silicone spatula, gently fold the dry ingredients into the egg mixture in two additions, taking care not to deflate the batter.
Stir about 1/4 cup of the batter into the melted butter until fully incorporated, then gently fold this buttered mixture back into the remaining batter until thick, silky, and shiny.
Cover and chill the batter in the refrigerator for 30–60 minutes.
Preheat the oven to 350°F (177°C). Brush a madeleine pan with the remaining 2 Tbsp (28g) melted butter (or use nonstick spray).
Spoon about 1 heaping tablespoon of batter into the center of each scalloped well of the pan.
Bake at 350°F (177°C) until edges are lightly golden, centers are set, and the characteristic hump forms. Do not overbake.
Cool briefly in the pan, then invert onto a rack. Dust with confectioners’ sugar and serve warm.