Preheat the oven to 350℉. Grease and line your pan with parchment paper and set aside.
Put your butter in a small saucepan over medium-low heat. Stir every 10-15 seconds with a metal whisk or silicone spatula. The butter will start to melt and foam, but over time the bubbles will get smaller and the butter will start to have a nutty aroma. Continue to cook the butter, stirring occasionally until brown bits at the bottom start to form. This will take about 10-15 minutes. Once butter is golden brown remove from heat. Burnt butter will change the taste of the brownies!
3/4 cups Unsalted Butter
Add the cocoa powder to the brown butter and whisk until no lumps remain.
3/4 cups Cocoa Powder
In a separate bowl, beat the eggs and brown sugar together until fluffy and pale.
3 Eggs, 1.5 cups Brown Sugar
Fold in the butter and chocolate mixture to the egg mixture with a spatula to combine. Stir in vanilla once combined.
1.5 tsp Vanilla Extract
Add the flour, espresso, and the salt and fold until no streaks remain. Add in the chocolate chips, if using, and stir. (I used milk chocolate chips this time, but feel free to use whatever chocolate you want! sometimes I use multiple types).
3/4 cups Flour, 1.5 tbsp espresso powder, 1/2 tsp Salt, 1/2 cup Chocolate chips, semi-sweet or milk
Pour mixture into the lined baking pan, smoothing out the top and sprinkling chocolate chips (optional). Place them in the oven and bake for roughly 30 minutes. Check the doneness by inserting a toothpick or knife in the center. Depending on your oven it may take up to 40 minutes.