Preheat the oven to 160c fan, 180c, 350f or gas mark 4
Melt the chocolate in a bowl over some gently simmering water.
Add the butter and melt that as well. Set aside to cool
In a separate bowl, mix together the flour, salt and sugar.
Once the chocolate mix is tepid, whisk in the eggs. If you try to whisk in the eggs while the chocolate and butter mixture is still hot, the eggs will scramble, ruining your chocolate blondie mixture. The mixture will probably thicken as you mix in the eggs.
Now tip in the the flour mixture and gently stir it all together.
Tip your lovely batter (it should look like a thick Yorkshire pudding mix) into your baking pan and bake for 20-25 minutes. Blondies should not be overcooked or you will have chocolate cake rather than blondies. They should be a little springy round the edges like a normal cake, but still gooey in the middle, with no wobble left.
Resist the urge to scoff them straight out of the oven and leave to cool, then cut them into whatever size you like. I usually cut brownies into 16 pieces.