Prepare your equipment:
Grease and lightly flour your madeleine pan, ensuring each cavity is coated. Preheat your oven to 375°F (190°C).

Mix the dry ingredients:
In a small bowl, whisk together the flour, baking powder, and salt. Set aside.

Whisk the eggs and sugar:
In a large bowl, beat the eggs and sugar with a hand or stand mixer on high speed until pale, thick, and fluffy (about 5 minutes).

Add the vanilla and zest:
Gently mix in the vanilla extract and lemon zest, if using.

Incorporate the cream:
Reduce the mixer speed to low and gradually pour in the heavy cream, mixing just until combined.

Fold in the dry ingredients:
Using a spatula, gently fold the dry ingredients into the wet mixture in two batches. Be careful not to overmix.

Add the butter:
Drizzle the melted butter over the batter and gently fold it in until fully incorporated.

Chill the batter:
Cover the batter and refrigerate for at least 30 minutes (or up to overnight). This helps the cookies form their signature hump.

Fill the pan:
Spoon or pipe the batter into the prepared madeleine pan, filling each cavity about ¾ full.

Bake to golden perfection:
Bake for 10-12 minutes, or until the edges are golden and the centers spring back when lightly touched.

Cool and serve:
Allow the cookies to cool in the pan for a few minutes before transferring them to a wire rack. Dust with powdered sugar before serving for an extra touch of sweetness.