Heat oven to 350 degrees. Line 24 muffin cups with paper liners.

Combine the flour, cocoa, baking soda and salt in a medium bowl. Whisk to blend. Combine the buttermilk and the vanilla in a measuring cup.

Beat the butter and the sugar in a medium mixing bowl with an electric mixer on medium high speed until light and fluffy. Add the eggs one at a time, beating well after each addition. Add the flour mixture alternating with the buttermilk mixture, starting and ending with the flour mixture.

Divide the batter between the prepared muffin pans. Bake until a toothpick inserted in centers comes out clean, 18 to 20 minutes. Transfer to a wire rack and cool 10 minutes. Invert and cool completely.

Filling and Swirl: Beat butter in a medium-size bowl until light and fluffy. Gradually add confectioners' sugar. Add 2 tablespoons of the milk and beat 5 minutes until almost white and light and fluffy. Add additional milk if mixture is too thick. Spoon frosting into a pastry bag fitted with a medium-size plain round tip. Remove cakes from pan. Insert tip of pastry bag into top of cakes, about 1/2 inch deep, and squeeze.

Meanwhile, make the Glaze: Heat the cream and corn syrup in a small saucepan over medium heat until it just comes to a boil. Remove from heat and stir in the chocolate chips. Cover and let stand 5 minutes. Whisk until smooth.

Dip the tops of the filled cupcakes into the chocolate glaze. Place on a cooling rack to set for 10 minutes.

Change the piping tip for the vanilla frosting to a smaller round tip. Pipe decorative swirls on top of the glazed cupcakes.