Ice cream divinity

I saw Ms. Lawson make this chocolate peanut butter sauce on a recently-aired episode of Nigella Express, and I knew that we too must make it in our house. My only changes were to make it with semi-sweet chocolate instead of milk and I used 1/2 and 1/2 instead of cream because that is what I had on hand. It came out well - and when poured hot over rock hard vanilla ice cream, it was delicious. The addition of salty peanuts would be a plus, had I had them on hand, but were not a necessity.