Prep the pan and oven. Heat the oven to 350°F (175°C). Line an 8-inch (20 cm) square pan with parchment, leaving overhang for easy lifting. Lightly grease the parchment.

Brown or melt the butter. In a medium saucepan over medium heat, melt the butter. For extra flavor, let it foam and brown, stirring, until it smells nutty and the milk solids turn golden. Remove from heat.

Melt the chocolate. Off the heat, add the chopped chocolate to the warm butter. Let sit 1 minute, then stir until smooth and glossy. If needed, return to low heat for a few seconds to finish melting.

Whisk in sugars. Add granulated and brown sugar to the warm mixture and whisk until combined. The batter may look grainy—this is fine.

Add eggs and vanilla. Whisk in eggs, one at a time, until the batter thickens and looks shiny. Mix in vanilla. Beat for about 30 seconds to encourage a crackly top.

Dry ingredients. In a small bowl, whisk flour, cocoa powder, espresso powder, and kosher salt. Fold gently into the wet batter just until no dry streaks remain. Don’t overmix.

Fold in nuts. Stir in about 3/4 cup of the chopped pistachios, reserving the rest for the top.

Pan and top. Spread the thick batter evenly in the pan. Sprinkle the remaining pistachios over the surface. Add a pinch of flaky sea salt if you like contrast.

Bake. Bake 22–28 minutes, until the edges are set and the center no longer jiggles. A toothpick should emerge with moist crumbs, not wet batter.

Cool completely. Let brownies cool in the pan on a rack for at least 1 hour. For clean slices, chill 30 minutes before cutting.

Slice and serve. Use the parchment to lift out. Cut into 9 large squares or 16 smaller bites. Enjoy as-is or warm slightly and top with vanilla ice cream.