Ashley's Mocha Madeleines

INGREDIENTS

• 3 large eggs
• 1/2 cup granulated sugar
• 1/2 teaspoon pure vanilla extract
• 3/4 cup all-purpose flour
• 1/4 cup cake flour (not self-rising)
• 1/4 cup best-quality cocoa powder, plus more for tins
• 1/2 teaspoon baking powder
• 1 tablespoon ground espresso (not instant)
• 1/4 teaspoon salt
• 4 ounces (1 stick) unsalted butter, melted and cooled, plus more for tins
• 2 1/4 cups confectioners' sugar, plus more if needed
• 1/4 cup brewed espresso or coffee, plus more if needed
• 1/2 teaspoon ground espresso (not instant)