01 -
Heat oven to 175°C / 350°F. Line a 20 cm square metal pan with baking paper, leaving an overhang.
02 -
Melt butter in a saucepan over low heat. Remove from heat and whisk in sugar and cocoa. Let cool until warm rather than hot.
03 -
Whisk in eggs one at a time, followed by vanilla and salt, until glossy. Fold in flour just until no dry patches remain.
04 -
Fold in 80 g walnuts. Spread batter in the pan and scatter the remaining 20 g walnuts over the surface.
05 -
Bake 25–30 minutes until the edges are set and a toothpick inserted in the center comes out with moist crumbs, not liquid batter.
06 -
Cool in the pan for at least 60 minutes before cutting into 16 squares. The middle should be dense and fudgy, not raw or runny.
07 -
Store in a covered container for up to two days at a cool room temperature, or refrigerate for up to five days. Freeze well-wrapped portions for up to two months.