Recipe(tried): Russian Potato Casserole with Caramelized Onions

This recipe is from Richard in Cincinnati. These are truly magnificent!!!! It's worth all the work that goes into making these potatoes.

RUSSIAN POTATO CASSEROLE WITH CARAMELIZED ONIONS

"These are killer. They always get vacuumed off the plate with the guests inquiring if there are more..."

FOR THE CARAMELIZED ONIONS:
6 large sweet onions, diced or sliced thinly
5 tbsp. butter
4 tbsp. olive oil
1 tbsp. sugar
FOR THE POTATOES:
About 4 lbs. of russet potatoes
Chicken stock
1 stick (1/2 cup) butter, not margarine
1 cup heavy whipping cream
3 cups sour cream, divided use
4 eggs, beaten to blend
1 tsp. dried dill weed

TO PREPARE THE ONIONS:
Melt the 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, stirring. The onions will take about an hour.

TO PREPARE THE POTATOES:
Meanwhile, boil the potatoes in enough chicken stock to cover. (Cook until slightly overdone for the best effect.) Drain the potatoes completely, reserving the chicken stock. Mash the potatoes. Add the butter, cut into pieces to melt.

Stir the beaten eggs into 1 cup sour cream. Add this to the hot potatoes, stirring in quickly to distribute the egg evenly as it cooks in the hot potatoes. Stir in the heavy 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.*

Grease a casserole dish with butter 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. Finally, cover the top with a layer of the remaining 2 cups sour cream.

Bake at 350 degrees F for 30-35 minutes, or until the top is lightly browned.

TO MAKE AHEAD:
I've put these together the day before, then brought them to room temperature and baked them.

*Be sure to add alot of the chicken stock because they dry out in the oven - add enough to make the potatoes soupy.

This recipe serves about 12 people. You will need a 4 or 5 qt. casserole dish for this recipe.