Preheat oven to 350 degrees F. Lightly coat 12 muffin cups with cooking spray.
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 medium mixing bowl beat butter with an electric mixer for 1 minute. Gradually add sugar mixture and mix until light and fluffy. Add egg and mix well then add in vanilla.
Alternate adding flour mixture and buttermilk to butter mixture until well combined.
Divide half of the batter among the prepared muffin cups using approximately 1 rounded tablespoon in the bottom of each muffin well. Add 4 -5 berries to the centre of each muffin, and spoon the remaining batter over berries in muffin cups.
Bake for 18 to 20 minutes or until a toothpick inserted near the centre comes out clean (turning after 10 minutes to evenly cook). Cool in pans for 5 minutes. Gently remove cupcakes from pans and cool completely on wire racks.
Prepare Chocolate Glaze (directions below).
In a small saucepan over low heat, melt butter then add cocoa and 2 tablespoons of water. Cook, stirring constantly, until mixture thickens. DO NOT BOIL. Remove from heat and add in vanilla. Gradually add icing sugar and beat with wire whisk until smooth. Add additional water, 1/2 teaspoon at a time until glaze is of desired consistency, just thin enough to drizzle. This makes about 3/4 cup of glaze, enough for 12 cupcakes.
Place cupcakes UPSIDE DOWN on a parchment-lined baking sheet. Drizzle glaze over cakes and chill about 20 minutes or until icing is set. If desired, place cakes on individual dessert plates prior to drizzling with the glaze. Garnish cakes with additional raspberries. Makes 12 cupcakes.
An alternative presentation would be to forego the glaze completely and dust cupcakes with icing sugar just prior to serving.