225g (1 cup) unsalted butter

60g (¾ cup) Dutch-process cocoa powder

400g (2 cups) granulated sugar

4 large eggs

2 tsp pure vanilla extract

120g (1 cup) all-purpose flour

1 tsp fine sea salt

½ tsp baking powder

Preheat oven to 175°C / 350°F. Line an 8×8 inch (20×20cm) metal pan with parchment, leaving overhang on two sides.

Melt butter in a large microwave-safe bowl in 30-second bursts, stirring between each, until fully melted. Cool in the bowl for 5 minutes.

Add cocoa powder and sugar to the cooled butter. Whisk vigorously for 1 full minute until smooth.

Add all four eggs and vanilla extract. Whisk vigorously for 60 seconds until the batter turns glossy and slightly thickened.

Add flour, salt, and baking powder directly to the bowl. Fold with a rubber spatula until no dry streaks remain — about 20 strokes. Stop immediately.

Pour into the prepared pan, smooth to the corners. Bake 25 to 28 minutes — toothpick in the center should come out with moist fudgy crumbs.

Cool in the pan on a wire rack for at least 1 hour. For cleanest cuts, refrigerate 30 minutes, then cut with a hot dry knife wiped between every cut.