Preheat the oven to 350℉/180℃. Grease an 8x8 inch square pan. For easy removal of the brownies, place parchment paper on the bottom and 2 sides of the pan. Grease again and then set side.
Doing a double boiler method, in a large heat-proof bowl add white sugar, 3/4 cups of the chocolate chips, and butter. Melt and stir on low to medium heat until well combined.
1 cup butter, 1 1/2 cups white sugar, 1 1/2 cups semi-sweet chocolate chips
Remove from heat and allow to cool for 10 minutes. Once warm and not hot, add in eggs and vanilla and whisk in.
4 eggs, 2 tbsp vanilla
Toss in the flour, baking powder, salt, and cocoa powder. Using a spatula, gently fold until no dry streaks appear. Don't overmix!
3/4 cups cocoa powder, 1 cup all-purpose flour, 1/2 tsp baking powder, 1/2 tsp salt
Add in chopped walnuts and remaining chocolate chips. Stir in a few times.
1/2 cup chopped walnuts, 1 1/2 cups semi-sweet chocolate chips
Transfer into the prepared pan and spread evenly. Sprinkle extra walnuts and chocolate chips if desired.
Bake the brownies for 45-50 minutes. A toothpick inserted should come out fudgy. If it is wet, it isn't ready yet. Continue to bake at 5 minute intervals until fudgy in the middle, and the edges are set.
The brownies continue to bake as they cool in the pan. Allow them to sit until cooled. Slice, and enjoy!
Store the brownies on your counter for 3 days or in the fridge in an airtight container for 7.