This recipe was at the top of the first search page, I went pretty much with it as written.  I keep a few bottles of Guinness tucked away in the cupboard for recipes that call for a dark beer.  We had a leg of lamb, bought during the last holiday and saved to the freezer, it’s not an everyday item at groceries in our neck of the woods.  The recipe insists on a shoulder, saying that a leg won’t ever become tender enough, but that is nonsense.  Maybe she was thinking mutton rather than lamb?  I had frozen peas but decided to leave them out, opting for a chive garnish for eye appeal.