- 6 tablespoons (3/4 stick) unsalted butter, melted, plus more for pan
- 1/2 cup all-purpose flour, (spooned and leveled)
- 1/2 cup whole-wheat flour (spooned and leveled)
- 1/3 cup unsweetened cocoa powder
- 1 1/4 teaspoons baking powder
- 1 teaspoon coarse salt
- 1/4 teaspoon baking soda
- 1 cup packed light-brown sugar
- 1 1/4 cups unsweetened applesauce
- 1 large egg
- 8 ounces semisweet chocolate, coarsely chopped
Preheat oven to 350 degrees. Butter an 8-inch square baking dish; line with parchment, leaving a 2-inch overhang on all sides. In a medium bowl, whisk together flours, cocoa, baking powder, salt, and baking soda.
In a large bowl, stir together sugar, applesauce, and egg. Place butter and 6 ounces chocolate in a heatproof bowl set over (not in) a pot of simmering water; stir until melted. Stir chocolate mixture into sugar mixture. Stir in flour mixture. Pour into pan and top with 2 ounces chocolate.
Bake until a toothpick inserted in center comes out with moist crumbs attached, 40 minutes. Let cool in pan on a wire rack. Use parchment to lift cake from pan and cut into 16 squares.
Store in an airtight container, up to 5 days.