Prepare chocolate mixture: In a medium bowl, stir together chopped chocolate, cocoa powder, and espresso powder. Set aside.
Brown the butter: In a small pan, heat butter until melted and the white milk solids separate out. Continue heating it on medium heat, stirring often, until the mixture bubbles, the milk solids turn brown, and it smells nutty.
Melt chocolate: Pour the hot browned butter (you'll end up with about 125g) into the bowl of chocolate. Stir until the chocolate has melted and the mixture is smooth and shiny. Set aside.
Prep: Preheat the oven to 350°F and line a 9x9" pan with parchment paper. Leave parchment paper overhangs on the edges to be able to remove the brownies from the pan later. Use metal binder clips to secure the paper to the pan. Set aside.
Whip egg mixture: In a large mixing bowl, add the eggs, granulated sugar, brown sugar, and miso paste. Use an electric hand mixer to beat this mixture on med-high speed for at least 5 minutes until it becomes thick and pale in colour.
Pour in chocolate mixture: With the mixer on low, stream in the melted chocolate mixture. Mix until combined.
Mix in flour: Finally, add the flour and fold it into the batter with a spatula until just combined.
Fill pan: Transfer the brownie batter to your lined pan. Use a spatula to push the batter into the corners and edges of the pan and smooth it into a flat layer.
Bake: Bake for about 23-25 minutes until the top is shiny and it barely jiggles when you shake the pan. Let the brownies cool in the pan for about 15 minutes before lifting the whole sheet out to cool on a wire rack. Slice the brownies into squares before serving.