You will need a tin measuring approximately 33 x 23 x 5½cm / 13 x 9 x 2¼ inches Preheat the oven to 180°C/160°C Fan/350°F/gas mark 4. Line your brownie pan — I think it's worth lining the sides as well as the base — with foil, parchment or Bake-O-Glide. Melt the butter and chocolate together in a large heavy-based pan. In a bowl or large wide-mouthed measuring jug, beat the eggs with the sugar and vanilla. Measure the flour into another bowl and add the salt. When the chocolate mixture has melted, let it cool a bit before beating in the eggs and sugar, and then the nuts and flour. Beat to combine smoothly and then scrape out of the saucepan into the lined pan. Bake for about 25 minutes. When it's ready, the top should be dried to a paler brown speckle, but the middle still dark and dense and gooey. And even with such a big batch you do need to keep alert, keep checking: the difference between gungy brownies and dry brownies is only a few minutes; remember that they will continue to cook as they cool.