Preheat the oven to 350 °.
Grease a square pan with the extra butter, then dust it with the extra flour. Set that aside.
In a pot, melt the stick of butter with half a bag of the chocolate chips. Keep stirring until completely melted. Take it out of the heat and set aside to cool completely.
In a mixer, beat the eggs, sugar and vanilla. Add the cooled melted chocolate. Keep mixing. Then add the flour and salt. Continue to mix until completely blended.
Fold in the nutella and remaining chocolate chips. Pour the whole thing into the buttered and dusted pan. Bake it in the oven for 35-40 minutes. Test by sticking a toothpick. When it comes out clean with a little bit of crumbs, the brownies are done.
Cool for a few minutes before cutting into squares.
