Preheat the oven to 350 degrees. Prepare two 9 x 13 inch baking pans with parchment paper, leaving an overhang of parchment on the 2 long sides of the pans.
In a small bowl, stir together flour, cocoa powder and salt. Set aside.
Combine melted butter and sugar in a large bowl, whisking to mix well.
Add eggs, one at a time, stirring well after each. Add vanilla and stir until incorporated.
Add 1 ½ cups of Nutella, again stirring well until completely mixed.
Stir the dry ingredients into the wet ingredients until the flour is just mixed in without overmixing.
Divide the batter evenly between the 2 pans and smooth the tops.
Bake the brownies for about 12-14 minutes until a toothpick inserted comes out almost clean with just moist crumbs.
Cool the brownies in the pan for 10 minutes and then transfer the pans to the freezer to chill for 30 minutes.
Before assembly, remove the ice cream from the freezer for about 20 -30 minutes to soften.
Once the brownies have chilled, scoop the ice cream over one pan of brownies. Using an offset spatula or knife, smooth the ice cream into an even layer.
Dollop the remaining ½ cup of Nutella over the ice cream evenly and swirl through the ice cream using a sharp knife.
Carefully remove the other brownie from the pan using the parchment paper to lift it out. Remove the parchment from the brownie and carefully place it on top of the ice cream, pushing it down slightly.
Place the pan into the freezer and freeze for about 2 hours until completely firm.
Once frozen, remove the pan from the freezer and cut the brownie ice cream sandwiches using a sharp knife into 18 squares.