Line a 9″ square aluminum baking pan with foil so that it is rising up past the edges of the pan, then grease it well. Preheat the oven to 350F.

In a small saucepan, heat the butter over medium heat until it has melted and begun to foam. Gently scrape the bottom with a rubber spatula to prevent it from burning. Continue to cook until it has stopped making noise– the liquid will pop a lot while it is evaporating, but will be quiet when it’s cooked off.

Once the butter has browned, remove it from the heat and add in the chopped chocolate. Stir it until it has all melted and set aside. Sift the cocoa powder and flour together and keep nearby.

In the bowl of a stand mixer fitted with a whisk, beat the eggs, sugars, salt, and vanilla together on medium-high for about 8 minutes, scraping the bowl occasionally to make sure everything is getting combined. The mixture should be very pale and thick when it’s done. 

Turn the mixer down to low and pour in the melted browned butter and chocolate while still mixing. Remove it from the mixer, add the flour and cocoa powder all at once and fold it in with a rubber spatula until it is all combined.

Pour the batter into the lined, greased baking dish and place in the oven on a rack in the middle of the oven. Bake for about 30 minutes, or until the center is just set. And if you have an internal thermometer, they are ready when the center measures 205F.

Remove them from the oven, then use the foil to lift the brownies out of the pan and onto a cooling rack. This stops the baking and allows them to cool faster.

Once the brownies have completely cooled, cut them into squares.