01 -
Preheat oven to 325°F. Spray a 9-inch square pan with nonstick spray and line with parchment paper, leaving 2-inch overhang on all sides.
02 -
In a medium saucepan over medium-low heat, melt butter, chopped chocolate, and 1 cup chocolate chips, stirring often until smooth. Set aside to cool.
03 -
Whisk together eggs, Nutella, sugar, and vanilla in a large bowl. Stir this mixture into the warm chocolate mixture.
04 -
Sift together flour, baking powder, and salt. Stir into the chocolate mixture. Fold in remaining chocolate chips and 1 cup hazelnuts.
05 -
Pour batter into prepared pan, sprinkle with remaining hazelnuts. Bake 40 minutes, then tent with foil and bake 10-15 minutes more until mostly set. Cool completely before cutting.