Boston Cream Pie Cupcakes

Preheat oven to 350°. Spray a standard-size (2½-inch) muffin pan with nonstick spray; set aside.

Whisk together 3 egg yolks in a medium saucepan. Whisk whole milk, granulated sugar, and corn starch. Bring to a boil, whisking constantly. Reduce heat to low; cook and whisk 1 minute. Remove from heat; whisk unsalted butter and 2 teaspoons vanilla extract. Transfer to medium bowl. Place plastic wrap on surface to cover; cool completely. Refrigerate custard until ready to use.

Prepare batter for extra-moist classic yellow deluxe cake mix according to pkg. directions using water, vegetable oil, and 3 eggs. Stir in sour cream and 1 teaspoon vanilla extract.

Pour batter into prepared muffin cups. Bake 18 to 21 minutes or until toothpick inserted in center of cupcakes comes out clean. Remove from muffin cups; cool completely.

Microwave heavy whipping cream and light corn syrup in medium microwave-safe bowl for 1½ minutes or until hot. Stir in chocolate chips; let stand 2 minutes. Whisk until completely smooth; set aside.

To assemble, split cooled cupcakes in half horizontally. Pipe or spread custard onto cupcake bottoms. Sandwich with cupcake tops. Spoon chocolate mixture on tops of cupcakes; spread evenly with back of spoon. Refrigerate until ready to serve.