Ingredients

• 1 cup all-purpose flour
• 1/3 cup unsweetened Dutch-process cocoa powder
• 1 teaspoon baking soda
• 1/2 teaspoon baking powder
• 1/4 teaspoon salt
• 1 stick unsalted butter, softened
• 1 cup packed light brown sugar
• 2 large eggs at room temperature 30 minutes
• 1 teaspoon pure vanilla extract
• 1 cup whole milk
• 1/4 cup heavy cream
• 3 1/2 oz bittersweet chocolate (not more than 60% cacao if marked), finely chopped
• 2 teaspoons light corn syrup
• Colorful confectionary sprinkles and/or nonpareils
• a 9- by 2-inch round cake pan

Instructions

1. Preheat oven to 350°F with rack in middle. Butter bottom and side of pan, then line bottom with a round of parchment.
2. Sift together flour, cocoa powder, baking soda, baking powder, and salt into a bowl.
3. Beat together butter and brown sugar in a large bowl with an electric mixer at medium-high speed until light and fluffy, 3 to 5 minutes. Add eggs 1 at a time, beating well after each addition, then beat in vanilla. Reduce speed to medium-low and add flour mixture and milk alternately in batches, beginning and ending with flour mixture (batter will appear curdled).
4. Transfer batter to cake pan and smooth top. Bake until cake begins to pull away from side of pan and a wooden pick inserted into center comes out clean, 35 to 40 minutes. Cool cake in pan 5 minutes, then invert onto a rack and cool completely, about 1 hour.
5. Bring cream to a simmer in a small heavy saucepan over medium heat, then pour over chocolate in a bowl and let stand 1 minute. Gently whisk until smooth, then stir in corn syrup. Cool completely, gently stirring occasionally, about 30 minutes (glaze will thicken).
6. Carefully peel off parchment from cake. Pour glaze onto center of cake and spread to edges with a spatula. Decorate with sprinkles and/or nonpareils.