Preheat the oven to 350°F (180°C) and place a rack in the middle of the oven.

Chop the chocolate into small pieces and set aside.

Let the butter melt in a medium saucepan over medium heat. Use a light-colored pan, as otherwise you will struggle to see the caramelization of the butter.

Once the butter melts, let it cook for around 3-4 minutes, regularly whisking.

Once it starts to foam, add in milk powder and whisk until it browns into a deep amber color and smells nutty and caramel-like.

Add the chopped chocolate to the hot butter and stir until the chocolate has melted.

Stir the sugars into the butter mixture, followed by the eggs and vanilla. Whisk well for 1-2 minutes until it is well combined.

Next, whisk the cocoa powder, espresso powder, and salt into the wet ingredients until well combined.

Finally, fold through the all-purpose flour and the chocolate chips into a thick chocolate batter.

Scoop the brownie batter into the prepared pan. Bake for around 28-32 minutes until a cake tester is inserted. It should have no wet batter but a few moist crumbs stuck to it.

Let the warm brownies cool completely in the pan before lifting them from the pan and placing them on a wire rack. For extra-clean brownie slices, chill them in the fridge before slicing. Sprinkle with a little optional flaky salt.

Store any leftover brownies at room temperature or in the fridge in an airtight container for up to a week.