Melt 225g (1 cup) butter. Set aside until tepid.

Sift together 125g (1 cup) cocoa powder, 70g (½ cup) flour, 2 tsp espresso powder, and ¾ teaspoon of sea salt in a large bowl.

In a separate small bowl, whisk together 4 eggs, 150g (¾ cup) granulated sugar, and 170g (¾ cup) brown sugar until light and airy.

Stir half of the egg mixture into the cocoa powder mixture, then stir in the melted butter. Stir in the remaining egg mixture.

Scrape the batter into a pan (either a 20cm square pan or a 22 x 33cm rectangular pan) which has been greased with softened butter and then dusted with flour (I also like to line the bottom with baking parchment). Smooth the top, and sprinkle liberally with flaky sea salt.

Bake the brownies in a 180c oven until the centre is almost set, about 20-25 minutes.

Let cool in the pan before decanting and cutting into squares.