• Preheat oven to 350F (175C) and line a 9x9’ (23x23cm) baking pan with parchment paper. Set aside.
• In a large, microwave safe bowl, melt your butter, then immediately whisk in the cocoa powder until smooth.
  8 Tablespoons (113 g) unsalted butter, ½ cup (50 g) Dutch cocoa powder
• Add sugar, eggs, and vanilla extract and whisk, well until batter is smooth.
  1 ¼ cups (250 g) granulated sugar, 2 large eggs, 1 teaspoon vanilla extract
• Add flour and salt then stir to combine.
  ¾ cup (94 g) all-purpose flour, ½ heaping teaspoon salt
• Stir in mini chocolate chips, if using.
  ¼ cup (45 g) mini chocolate chips
• Transfer to center rack of 350F (175C) preheated oven and bake for 23 minutes, until a toothpick inserted into the center comes out clean or with a few moist, fudgy crumbs.
• While the brownies cool, prepare your frosting.

Make the frosting

• In a medium saucepan, combine chopped chocolate, butter, and milk over low heat and stir until melted. Don’t panic if your mixture looks separated or even oily, it will come together in the next step.
  3 oz (85 g) unsweetened chocolate, 4 Tablespoons (57 g) salted butter, ⅓ cup (80 ml) whole milk
• Remove from heat and whisk in salt and vanilla extract.
  ¼ teaspoon salt, 1 teaspoon vanilla extract
• Allow the chocolate mixture to cool for several minutes (3-5), then whisk in powdered sugar until frosting is smooth and glossy. Allow frosting to cool slightly, whisking occasionally, until it has thickened – it is ready to spread over the brownies when it begins to lose its shine, and no longer drips off the spoon or whisk but is still spreadable (see note).
  2 ½ cups (312 g) powdered sugar
• Spread frosting over brownies (it’s OK if they’re still a bit warm), allow the fudge to set completely, then slice and enjoy.