Cheesy Herbed Mashed Potatoes

3 lbs baking potatoes (about 4 large), peeled and quartered
1/2 stick butter
3/4 C minced onion
1 T chopped fresh or 1 tsp dried basil
1 T chopped fresh or 1 tsp dried chives
1 T chopped fresh or 1 tsp dried dill weed
1 tsp salt
1/2 tsp black pepper
1 1/2 C (6 oz) shredded mild Cheddar cheese (see note)
1/2 C milk

In a large pot of boiling salted water, cook potatoes 20 to 25 minutes, or until tender; drain. Place butter and scallions in pot and cook over medium heat one minute. Reduce heat to low and stir in basil, chives, dill, salt, and pepper. Return drained potatoes to pot; add cheese and milk. Remove from heat and mash with a potato masher or beat with an electric mixer until smooth.