Make Ahead Fluffy Mashed Potato Casserole

Now:
2 cups mashed potatoes
1 cup cream cheese, softened (8 oz)
1 small onion, finely chopped
2 eggs, lightly beaten
2 T. flour
Salt and pepper
Later:
One can French fried onions (2.8 oz)

In large bowl, combine potatoes, cream cheese, onion, eggs and flour. With a mixer on medium speed, mix until blended. Increase the speed to high and beat the potato mixture until it's light and fluffy. Season with salt and pepper and mix well. Cover and refrigerate for 8 hours or up to 2 days.
Later:
Remove potato mixture from refrigerator. Let it sit for up to 1 hour. Preheat oven to 325. Put potato mixture in a greased 3 quart casserole dish. Spread French fried onions on top of the potatoes mixture and bake for 30 to 40 minutes, until bubbly. Serves 4