Preheat oven to 180 C Line a 8x8 pan with foil, leaving an overhang on two opposite sides.
Melt chocolate and butter in a bowl over a pot of barely simmering water until smooth, stirring often.
Remove bowl from heat and stir in sugar vanilla and salt.
Add eggs one at a time, stirring thoroughly.
Stir in flour and beat with a spoon or rubber spatula for a minute or two until smooth and glossy.
Stir in nuts.
Scrape batter into prepared pan and smooth to even it.
Bake for 30 to 35 minutes. A toothpick inserted in the center should come out with some thick gooey batter clinging to it.
