Preheat oven to 375°F (190°C). Grease and lightly flour a madeleine pan.

In a large mixing bowl, whisk together sugar and eggs until pale and slightly thickened.

Add vanilla extract and stir to combine.

In another bowl, sift together flour, cocoa powder, baking powder, and salt.

Gently fold the dry ingredients into the egg mixture until just combined.

Fold in the melted, cooled butter until the batter is smooth.

Cover and refrigerate for at least 30 minutes to help form the signature hump.

Spoon the batter into the prepared pan, filling each mold about three-quarters full.

Bake for 10–12 minutes, or until edges are set and centers spring back when lightly pressed.

Remove from the pan immediately and cool on a wire rack.

Dust with powdered sugar before serving.