Melt the 5 tablespoons butter in a large skillet or Dutch oven. Add the oil and heat. Add the onions, stir to coat and reduce the heat to low. Cook the onions, stirring occasionally, until they turn a deep brown color. Sprinkle with the sugar and continue cooking for a few more minutes. The onions will take about an hour.
Meanwhile, boil the potatoes in enough chicken stock to cover. (Cook potatoes until slightly underdone) Drain the potatoes completely, reserving the chicken stock. Mash the potatoes. Add the butter. Stir the beaten eggs into one cup of the sour cream. Add this to the hot potatoes, stirring quickly to distribute the egg evenly. Stir in the cream and the dill weed. Add enough of the reserved stock to make a very loose mashed potato consistency. You do not want them to be stiff because they will dry out in the oven.
Butter a casserole dish and add half the potatoes. Spread the caramelized onions in an even layer over the potatoes. Carefully cover the onions with the rest of the potatoes, sealing them in. Cover the top with the remaining 2 cups of sour cream. Bake at 350F for 30-35 minutes or until the top is lightly browned.