Preheat the oven to 350 degrees.
Butter and line parchment paper onto a 9 X 13" light metal baking pan.
In a small saucepan over low heat on the stove, melt butter completely.
Stir in sugar and stir consistently for 2 minutes on low heat. Do not boil.
Remove sugar-butter mixture from the heat and stir in the Nutella until well blended.
Using a kitchen stand mixer or by hand, pour the mixture into a large mixing bowl and blend in the cocoa powder, eggs, salt, baking powder, and vanilla extract. Stop immediately when all ingredients are just combined.
Stir in the flour and chocolate chips until just combined and no more.
Spread the batter into the prepared baking pan. It is supposed to be thick and sticky.
Bake for 35 minutes and no more. A tester should come out clean. The edges will be firm and the center and top of the brownie will be shiny and look moist.
Remove immediately from the oven and cool on a wire rack for about 10 minutes and then place in the fridge for a half-hour to an hour to completely chill the brownie.
With a sharp, serrated knife, with one smooth cut, slice the brownies, using a damp cloth to wipe the knife between slices.
