Preheat oven to 350 degrees F. Line a 9x13 inch pan with parchment paper. For thinner brownies, use two 7x11 inch brownie pans and preheat to 325F.
Mix all ingredients except chocolate chips in a large bowl and beat until smooth. A stand mixer with the paddle attached makes the job even easier, as does strong arm muscles.
Spread mixture evenly in the pan by tilting it back and forth. The batter should be Sprinkle the top with chocolate chips and hazelnuts.
Bake in the 9x13 inch pan at 350 degrees for 30 minutes. If using two 7x11 inch brownie pans (or halving and using one), bake at 325 degrees F. for 25 minutes or until the internal temperature tops out at about 200F.
Let the brownies cool at room temperature.
Swirl Option
If you'd like to swirl Nutella or peanut butter through, mix about ¼ cup of Nutella with 1 ½ teaspoons oil. Drop dollops over the batter and very lightly swirl. The oil will help keep it from drying up.
Notes
If you happen to have some Frangelico, you can use 1 teaspoon of vanilla plus 2 tablespoons of Frangelico another liqueur.