Step 1Place the potatoes in a large saucepan with water to cover by about 1 inch and a pinch of salt. Cover and bring to a boil, then reduce the heat and simmer until the potatoes are very tender, about 35 minutes. Drain and set aside until cool enough to handle.
Step 2In a large, heavy skillet, heat 2 tablespoons oil over medium heat. Add the onions and cook, stirring occasionally, until they are tender and golden brown, about 30 minutes. Remove from heat and cool 1 minute, then stir in the garlic.
Step 3Heat the oven to 350 degrees. Peel the potatoes while still fairly hot. Cut them in a few chunks. Mash them thoroughly with a potato masher, not in a food processor. Add the fried onion and garlic mixture and the remaining 2 tablespoons of oil, and mix well.
Step 4Add one-third cup sour cream and three-eighths teaspoon nutmeg, or as desired, and salt, pepper and cayenne to taste. Add beaten eggs and mix well.
Step 5Thoroughly grease a 2-quart casserole with olive oil. Add the potato mixture and smooth the top thoroughly. Bake the kugel uncovered until it is firm, about 40 minutes. The kugel can be made ahead of time up to this point, then refrigerated up to 2 days before serving; to finish, reheat (covered with foil) in a 300-degree oven before continuing with the recipe.
Step 6Shortly before serving, heat the oven to 450 degrees. Season the remaining 1 cup sour cream with the remaining one-eighth teaspoon nutmeg, or to taste. Spoon the sour cream mixture over the kugel in dollops, and spread it gently to the edges of the kugel; try not to spread the sour cream to the sides of the pan. Sprinkle the sour cream evenly with the grated cheese, then with paprika.
Step 7Bake the kugel until the topping sets and browns lightly, about 10 minutes.
Step 8If you would like a browner topping, broil the kugel, checking often, no longer than 1 minute, until the topping is dotted with brown. Serve hot.