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.
In a mixer using the whisk attachment, beat the eggs, extra yolk, granulated sugar, powdered sugar, glucose, brown sugar, and vanilla on high speed for 6–8 minutes until thick and pale.
With the mixer on low, slowly add the 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.
Preheat the oven to 150°C. Line an 8×8-inch baking pan with parchment paper, leaving some overhang. Pour in the batter tap the pan once on the counter to release air bubbles.
Bake for 12-13 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 30 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.
