Turn raspberry-filled cupcakes upside down before drizzling with a rich chocolate truffle icing.
Let butter and eggs stand at room temperature for 30 minutes. Meanwhile, preheat oven to 350 degrees F. Lightly coat twenty-four 2-1/2-inch muffin cups with nonstick cooking spray; set aside.
In a medium bowl, stir together flour, cocoa powder, baking soda, baking powder, and salt. In a small bowl, combine granulated sugar and brown sugar. Set aside.
In a large bowl, beat butter with an electric mixer on medium to high speed for 30 seconds. Gradually add sugar mixture, about 1/4 cup at a time, beating on medium speed about 5 minutes or until light and fluffy, scraping side of bowl occasionally. Add eggs one at a time, beating well after each addition. Beat in vanilla.
Alternately add flour mixture and buttermilk to butter mixture, beating on low speed after each addition just until combined. Beat on medium to high speed for 20 seconds more.
Divide half of the batter among the prepared muffin cups. Divide the 2 cups raspberries among muffin cups, adding 3 or 4 berries to the center of each cup. Spoon the remaining batter over berries in muffin cups.
Bake for 18 to 20 minutes or until a toothpick inserted near the centers comes out clean. Cool in pans on wire racks for 5 minutes. Remove cupcakes from pans; cool completely on wire racks.
Prepare Chocolate Truffle Icing. To glaze cupcakes, invert one cake at a time onto a slotted spoon. Hold the cake over the bowl of icing and spoon icing over cake, allowing excess to drip down side. Place glazed cakes on a wire rack set on a parchment-lined baking sheet. Chill about 20 minutes or until icing is set. If desired, garnish cakes with additional raspberries. Makes 24 cupcakes.
To make 1 cup sour milk, place 1 tablespoon vinegar or lemon juice in a glass measuring cup. Add enough milk to make 1 cup total liquid; stir. Let stand for 5 minutes before using.