FOR THE CAKE: – 1 & 1/4 cups (150g) all-purpose flour – 1/2 cup (42g) unsweetened natural cocoa powder – 1/2 teaspoon baking powder – 1/2 teaspoon salt – 1/2 cup (113g) unsalted butter, softened – 1 cup (200g) granulated sugar – 3 large egg – 1 & 1/2 teaspoons vanilla extract – 1/2 cup (118ml) milk – 1/2 cup (85g) dark chocolate chip FOR THE GLAZE: – 1 tablespoon unsalted butter – 1 ounce (28g) unsweetened chocolate, roughly chopped – 1/2 cup (55g) confectioners' sugar, sifted – 1 to 1 & 1/2 tablespoons boiling water – chocolate sprinkles, toasted nuts, chocolate chips, or another garnish (optional)