Firstly, brown the butter- In a large pot (much larger than the butter amount you want to brown), turn it on to Medium to Medium-High heat, and then put in the butter. Stay close, and stir often. It will bubble, then foam. When it foams you will notice it climbing the pan, make sure to keep stirring at this point so it doesn't burn. Once the butter solids have turned brown, remove from heat.
Add brown sugar & stir until combined. It may look a little greasy at this point, but that is normal.
Add the chocolate chips and stir to melt with the warm butter and sugar. Set this aside while you continue with the dry ingredients.
Secondly, Mill the flour.
Then, add salt, baking powder, and cocoa powder to the flour, and whisk together to incorporate.
Preheat Oven to 350*F
Grease or line a 9x13 pan. (You can bake in a 8x8 for thicker brownies, bake longer - see directions below.)
Put butter, sugar, chocolate mixture into a stand mixer, and mix. Check the temperature of the mixture and make sure it is under 130*F (so you don't cook the eggs.)
Add vanilla extract and mix, then add eggs and mix to combine. (Don't over mix, because it will make it more of a cake mixture if you add too much air into the mixture.)
Then, add the dry ingredients, and mix just until combined. Don't overmix here either.
If you wanted to add any optional add-ins like more chocolate chips, nuts, or etc now would be the time to add those in.
Pour & spread the brownie batter into your prepared pan.
Bake for 20-30 minutes, until a tooth pick comes out clean. the edges should just be starting to separate from the pan. (Bake for 30-40 minutes for an 8x8 pan.)
Allow to cool, then cut. They will setup more as they cool as well.