Nonstick cooking spray
1 package (18.25 ounces) butterrecipe chocolate cake mix, Betty Crocker®
1⁄4 cup brown sugar, Domino®/C&H®
11⁄4 cups chocolate hazelnut spread, Nutella®
1⁄2 cup (1 stick) butter, melted
1 package (2.25 ounces) chopped hazelnuts, Diamond of California®
3⁄4 cup powdered sugar, Domino®/C&H®
1⁄4 cup heavy cream
Preheat oven to 350°F. Spray a 9-inch square baking pan with cooking spray; set aside.
In a large bowl, stir together cake mix and brown sugar. Add 1⁄2 cup of the chocolate hazelnut spread, the melted butter, and eggs; stir until combined (batter will be thick). Stir in hazelnuts. Pour into prepared baking pan.
Bake for 35 to 40 minutes or until a toothpick inserted in center comes out clean. Cool in pan on a wire rack.
In a medium mixing bowl, beat the remaining 3⁄4 cup chocolate hazelnut spread, the powdered sugar, and cream with an electric mixer on medium until smooth. Spread on cooled brownies.