4 cans (14-1/2 ounces each) chicken broth or 8 cups water plus 8 teaspoons chicken bouillon granules
3 cups sour cream, divided
1 cup heavy whipping cream
4 large eggs, beaten
1 teaspoon dill weed
In a large skillet, saute onions in oil and 1/3 cup butter until softened. Stir in sugar. Reduce heat to medium-low; cook, stirring occasionally, for 40 minutes or until deep golden brown.
Meanwhile, place potatoes in a large saucepan and cover with broth. Bring to a boil. Reduce heat; cover and cook for 15-20 minutes or until tender. Drain potatoes; transfer to a large bowl. Add 1 cup sour cream, the cream, eggs, dill and remaining butter. Beat until mashed.
Spread half of potatoes into a greased 13-in. x 9-in. baking dish; layer with onions and remaining potatoes. Gently spread remaining sour cream over the top. Bake, uncovered, at 350° for 30-35 minutes or until a thermometer reads 160°.