Chocolate Pistachio Fudge

I'm barely half-through my Christmas Present list, and the presents look more and more desperate. Today's hugely simple recipe, courtesy of Mein Lieblings TV Chef Nigella Lawson, is Chocolate Pistachio ( pis-ta-key-o) Fudge, made without the insane faff of sugar thermometers, but condensed milk.
When I read the ingredients I was shocked at the chocolate content, but after trying a few squares I could tell it wouldn't survive with sweet milk chocolate- it has to be good and dark. The pistachios don't add much flavour, but add a lot of texture and a gorgeous fleck of green.
1)Melt 350g of 70% dark chocolate with 1 397g tin of condensed milk and a knob of butter over a gentle heat. I've become embarrassed to say that I now use good-quality baking chocolate rather than real chocolate because I'm so dire at melting it I would burn anything that's not reinforced against my incompetence. In the meantime, bash some pistachios in a freezer bag until in smaller chunks. Mix with your melted chocolate, then pour the mixture into a foil or grease-proof paper lined baking tray and leave to cool before setting in the fridge. Cut into squares and give stingy handfuls to your recipients. It is very rich. You can tell them that.