Sweet and Red Potato Casserole
5 tbsp butter or margarine, divided
2 large sweet onions, chopped
2 tsp sugar
2 1/2 lb red potatoes, peeled and cubed
2 1/2 lbs sweet potatoes, peeled and cubed
1 1/2 cup milk, divided
1/4 cup sour cream
1 1/2 tsp salt, divided
1/2 tsp pepper
Melt 1 tbsp butter in a large skillet over medium heat. Add onions and sugar. Cook, stirring often, 25-30 minutes, or until onions are deep golden brown.
Meanwhile place red potatoes in enough water to cover them in a Dutch oven. Bring to a boil and reduce heat to medium. Simmer 20 minutes, or until tender. Drain. Repeat with sweet potatoes.
Preheat oven to 350 degrees. Spray a 3 quart casserole with non stick spray. Beat red potatoes, at medium speed until smooth. Add 3/4 cup milk, sour cream and 2 tbsp butter. Beat until smooth. Stir in 1 tsp salt and pepper. Spoon into casserole dish.
Beat sweet potatoes until mashed. Add remaining 3/4 cup milk and remaining 2 tbsp butter. Stir in remaining 1/2 tsp salt and pepper. Beat until smooth. Spoon over red potatoes. Top with 1/2 onion mixture; mix gently to combine in a swirl pattern. Top with remaining onion mixture.
Cover, bake 25-30 minutes or until thoroughly heated.