Layer the onion and garlic in the bottom of a crock pot.
Brown roast on all sides (about 3 minutes a side) and then place in crockpot. This is optional.
Sprinkle salt over roast. Place butter on top of roast. Lay the fresh sprigs of herb on top of butter.
Cook on low until the roast is tender and flakes when prodded with a fork. This usually takes 6-8 hours in my crockpot.
