Preheat the oven to 180C/350F/Gas 4.
Begin by chopping the nuts roughly, not too small, then place them on a baking sheet and toast them in a preheated oven for 8 minutes exactly. Please use a timer here otherwise you'll be throwing burned nuts away all day!
While the nuts are cooking, put the chocolate and butter together in a large mixing bowl fitted over a saucepan of barely simmering water, making sure the bowl doesn't touch the water.
Allow the chocolate to melt, then beat it until smooth, remove it from the heat and
simply stir in all the other ingredients until thoroughly blended.
Now spread the mixture evenly into the prepared tin and bake on the centre shelf of the oven for 30 minutes or until it's slightly springy in the centre.
Remove the tin from the oven and leave it to cool for 10 minutes before cutting into roughly 15 squares. Then, using a palette knife, transfer the squares on to a wire rack to finish cooling.