Preheat oven to 350°F and grease a 1qt casserole dish
In a sauce pan, heat the butter and add the onions. Saute until onions are translucent.
Stir the soup into the saucepan and add one cup of shredded cheese, reserve the remaining cheese for the top of the casserole. Stir the soup, onions, cheese, salt and pepper until warm and smooth. Remove from heat.
Place a layer of tots in the bottom of the dish, and pour half of the soup mixture overtop. Add the remaining tots and pour the balance of the soup evenly over the dish.
Cover with aluminium foil and bake for 40 minutes, or until bubble and potatoes are tender. Remove from oven, sprinkle remaining 1/3 cup of cheese over the top and return to the oven for 5 minutes uncovered.