Chocolate Sour Cream Bundt Cake

1 tablespoon butter, melted

1 tablespoon cocoa

3/4 cup natural cocoa (not Dutch-processed, 2 1/4 ounces)

6 ounces bittersweet chocolate, chopped

1 teaspoon instant espresso powder (optional)

3/4 cup water (boiling)

1 cup sour cream, room temperature

1 3/4 cups unbleached all-purpose flour (8 3/4 ounces)

1 teaspoon salt

1 teaspoon baking soda

12 tablespoons unsalted butter, room temperature

2 cups packed light brown sugar (14 ounces)

1 tablespoon vanilla extract

5 large eggs, room temperature

confectioners' sugar, for dusting (optional)

Using a pastry brush, coat all interior surfaces of a 12-cup Bundt pan with the butter. Dust with the cocoa, being sure to coat the entire pan thoroughly. Adjust oven rack to lower-middle position; preheat oven to 350°F.

Combine cocoa, chocolate, and espresso powder in a medium heatproof bowl; pour boiling water over and whisk until smooth. Cool to room temperature; whisk in the sour cream. In another bowl combine the flour, salt, and baking soda and whisk to combine.

In a standing mixer fitted with the flat beater, beat butter, sugar, and vanilla on medium-high speed until pale and fluffy, about 3 minutes. Reduce speed to medium and add the eggs one at a time, mixing for 30 seconds after each addition and scraping down bowl with rubber spatula after each addition. Reduce speed to medium-low (batter may appear curdled); add about one third of flour mixture and half of chocolate/sour cream mixture and mix until just incorporated, about 20 seconds. Scrape down the bowl and repeat using half of remaining flour mixture and all of the remaining chocolate mixture. Add the remaining flour mixture and beat until just incorporated, about 10 seconds. Scrape bowl and mix on medium-low speed until the batter is thoroughly combined, about 30 seconds.

Pour the batter into the prepared Bundt pan. Bake until a toothpick inserted in the center comes out with few crumbs attached, 45 to 50 minutes. Cool in the pan 10 minutes, then invert cake onto a wire rack with a piece of parchment on it; cool to room temperature. Dust with confectioners' sugar if desired before serving.

Adapted from Cook's Illustrated