Brown the Butter

• Melt the butter in a saucepan over medium heat. Add milk powder if using and stir continuously. Once the butter foams, sizzles, then settles down, continue stirring until golden brown with a nutty smell (about 3–5 minutes). Turn off the heat and stir in cocoa powder, chopped chocolate, and oil until smooth. Let it cool slightly.
  ¾ cup Unsalted butter, ¾ cup Dutch process cocoa powder, 4 oz 70% dark chocolate, chopped, 2 tablespoons neutral oil, 1 tablespoon milk powder
• In a large bowl, beat the eggs, extra yolk, granulated sugar, powdered sugar, brown sugar, and vanilla on high speed for 6–8 minutes until thick and pale. This step helps achieve the crackly top.
  3 large eggs, ¾ cup granulated sugar, 1 cup powdered sugar, ¼ cup light brown sugar, 1½ teaspoons vanilla extract, 1 egg yolk
• With the mixer on low, slowly add the warm (not hot) chocolate-butter mixture into the whipped eggs. Mix until just combined.
• Gently fold in the flour, salt, and espresso powder with a spatula. If the batter is still warm, let it sit for 5 minutes before folding in the chocolate chips.
  ½ cup all-purpose flour, ½ teaspoon salt, 1 teaspoon instant espresso powder, 1 cup semi-sweet or dark chocolate chips or chunks
• Preheat the oven to 350°F. Line an 8x8-inch metal baking pan with parchment paper, leaving some overhang. Pour in the batter and smooth the surface. Tap the pan once on the counter to release air bubbles.
• Bake for 28–32 minutes, or until a toothpick inserted comes out with moist crumbs. For added fudginess, tap the pan again right after baking.
• Let brownies cool in the pan for 90 minutes, or chill in the fridge for 1 hour. Lift out using parchment and slice with a sharp knife, wiping the blade clean between each cut.