Minimum 65% cocoa, and that is easily accessible and not too expensive. A good one is Trader Joes 3-pk Belgian Dark Chocolate (~$2.00 for 3 bars). I also like Dove Dark Chocolate squares.... I haven't really tried the fancy stuff yet.
A roasted boneless leg of lamb makes an impressive centerpiece for your table, but this recipe is easy enough to pull off any time. A classic gremolata perfumes the lamb; the mixture of garlic, lemon, and parsley holds its own against the strong flavor of the meat.