In a large skillet cook onion and garlic in hot butter over medium heat about 5 minutes until nearly tender. Add pot roast with juices. Bring to boiling; reduce heat. Simmer, covered, about 10 minutes or until pot roast is heated through.
Transfer pot roast to a serving platter, reserving juices in skillet. Stir basil into skillet; season to taste with salt and pepper. To serve, pour juices over pot roast.