Lamb Tops - tough
Bought 5 lamb tops at Dewars and I marinated them and cooked them according to directions and they looked great medium rare inside, but they were tough. I was told they were sirloin from top of the lamb and would be tender. I had 15 people for dinner and was so disappointed has anyone else had a problem like this with lamb tops.
Lamb top sirloin butt from the hindsaddle of the lamb is often cut into steaks or chops, or you can purchase them as a whole top sirloin butt from the butcher. The cut can be braised for maximum tenderness, or roasted to medium rare as you did. A lamb sirloin, on the other hand, is usually cut into steaks or chops and can be just a tender as beef tenderloin, while the top butt is comparable to beef sirloin, lean, flavorable and relatively tender.
I can't tell you why your roast was tough; it's normally a tender but lean cut. Did you slice it thinly across the moderate grain? I'm not familiar with Dewars, how is the quality of their meats? Was it imported or domestic lamb? How was it packed, cryo or dry aged?
Here's a little more info on your cut, but it doesn't solve the chewy issue: