1 cup whole-wheat pastry flour
3/4 cup rolled oats
1/2 teaspoon baking soda
1/4 teaspoon kosher salt
6 tablespoons unsalted butter, melted and slightly cooled
1 large egg
3/4 cup packed light brown sugar
1/2 cup unsweetened applesauce
3/4 cup semisweet mini chocolate chips
Preheat the oven to 350 degrees F. Line the bottom of a 9-inch square baking pan with a foil strip long enough to overhang on 2 opposite sides. Spray the foil lightly with cooking spray; set aside.
Whisk together the flour, oats, baking soda and salt in a medium bowl; set aside. Whisk the butter, egg, brown sugar and applesauce in a large bowl until combined. Add the dry ingredients to the wet and mix until barely mixed. Stir in the chocolate chips.
Spread the batter in the prepared baking pan. Bake until the cake is light brown around the edges and a toothpick inserted in the center comes out clean, 25 to 30 minutes. Remove from the oven and let cool on a rack for 15 minutes. Use the foil overhang to lift the cake out of the pan and let cool completely on the rack. Invert onto a plate and peel the foil off. Re-invert the cake onto a cutting board, cut into 12 pieces and serve.