3 tablespoons unsalted butter, softened
3/4 cup sifted all-purpose flour
1/3 cup unsweetened cocoa, preferably Dutch process
1/2 teaspoon baking powder
1/2 teaspoon salt
1 cup dark brown sugar
1 large egg
1 teaspoon pure vanilla extract
1 ounce semisweet chocolate, melted
1/4 cup unsweetened applesauce
Preheat the oven to 350°. Butter a 9-inch square baking pan with 1/2 teaspoon of the butter. Sift together the flour, cocoa, baking powder and salt.
Using an electric mixer, beat the sugar and the remaining butter. Add the egg and vanilla and beat until fluffy. Beat in the chocolate, then the applesauce. Beat in the dry ingredients on low speed until combined. Spread the batter in the prepared pan. Bake for about 25 minutes, or until a toothpick inserted in the center comes out clean. Let cool, then cut into squares.