Seriously. Best ever. Also the easiest! You gotta know that I'd never choose ease over taste, so really the easiest is more of a bonus than an actual feature.
Here's what I do.
1. Remove leg of lamb (bone in/bone out, whole/half...whatever you've got) from the freezer.
2. Make a paste of crushed garlic, salt (kosher works great, but not necessary), pepper and rosemary (I use dried because that's all I've ever got).
3. Rub the paste on the lamb.
4. Put the lamb in your crock pot.
5. Mix 3 parts water with 1 part balsamic vinegar.
6. Pour this into the crock pot.
7. Turn crock pot on high.
8. Come back 5-6 hours later and eat the delicious lamb!