Death by Chocolate Cupcakes

Makes 18 cupcakes
2-1/4 cups crushed chocolate sandwich pieces (such as Oreos), in 1/2 to 1/4- inch pieces (about 20 cookies)
1 cup (6 ounces) bittersweet chocolate chips
3 ounces bittersweet chocolate, chopped
Cupcake batter:
3 ounces unsweetened chocolate, chopped

1/2 teaspoon baking powder
1/2 teaspoon baking soda
1/4 teaspoon salt
1/2 cup (1 stick) unsalted butter, at room temperature
1-1/4 cups sugar
2 large eggs
1 teaspoon vanilla extract
1/2 cup sour cream
1/2 cup water

Position a rack in the middle in the middle of the oven. Preheat the oven to 350 degrees F. Line 18 muffin tin cups with paper cupcake liners.

Put the unsweetened chocolate in a heatproof bowl or the top of a double boiler and place it over, but not touching, a sauce pan of barely simmering water (or the bottom of the double boiler). Stir until the chocolate is melted and smooth. Remove from the water and set aside to cool slightly.

Sift the flour, baking powder, baking soda, and salt into a medium bowl and set aside.

In a large bowl, using an electric mixer on medium speed, beat the butter and sugar until smoothly blended and creamy, about 2 minutes. Stop the mixer and scrape the sides of the bowl as needed during mixing. On low speed, mix in the melted chocolate. On medium speed, add the eggs one at a time, mixing until each is blended into the batter. Add the vanilla and beat until the mixture looks creamy and the color has lightened slightly, about 1 minute. Mix in the sour cream until no white streaks remain. On low speed, add half of the flour mixture, mixing just to incorporate it. Mix in the water. Mix in the remaining flour mixture until it is incorporate and the batter looks smooth.

Spoon 1 tablespoon of the cookie pieces into the bottom of each paper liner, then spoon about 2 teaspoons of chocolate chips (about 8 chocolate chips) over the cookie pieces in each liner. Spoon a scant 1/4 cup of batter over the chocolate chips. Sprinkle the remaining chocolate chips and cookie pieces over the tops, pressing them gently into the batter.

Bake just until the tops feel firm and a toothpick inserted in the center comes out clean, about 22 minutes. Cool the cupcake for 20 minutes in the pans on a wire rack.

Holding an edge of each cupcake liner, carefully lift the cupcakes from the pan and place them on a wire rack to cool completely. (Removing the cupcakes from the pan this way prevents the soft chocolate chips from getting squashed.)

Put the chopped bittersweet chocolate in a heatproof bowl of the top of a double boiler and place it over, but not touching, a saucepan of barely simmering water (or the bottom of the double boiler). Stir until the chocolate is melted and smooth. Remove from the water and set aside to cool slightly.

Use a small spoon to drizzle thin lines of melted chocolate over the top of each cooled cupcake.

The cupcakes can be covered and stored at room temperature for up to 3 days.