For the Dark Chocolate Cupcakes:

1/2 cup unsalted butter, cut into 4 pieces
2 oz bittersweet chocolate, finely chopped
1/2 cup Dutch-processed cocoa
3/4 cup all-purpose Gold Medal flour
1/2 teaspoon baking soda
3/4 teaspoon baking powder
2 large eggs, at room temperature
3/4 cup granulated sugar
1 teaspoon vanilla extract
1/2 teaspoon salt
1/2 cup plain Greek yogurt or sour cream (I used Chobani Greek yogurt)

For the Raspberry Buttercream Frosting:

3/4 cup unsalted butter, at room temperature
2 cups powdered sugar
1 cup fresh raspberries
1/2 teaspoon pure vanilla extract
Additional fresh raspberries, for garnish-if desired