Sweet Potatoe Casserole

3 cups sweet cooked mashed potatoes
1/3 cup packed brown sugar
1/3 cup eggnog
2 tbsp melted butter
1 tsp vanilla extract
1/2 tsp salt
2 egg whites
1/2 cup packed brown sugar
1/4 cup flour
2 tbsp butter

Preheat oven to 350F. Coat a 2 qt casserole dish with non-stick spray. Combine the mashed potatoes, 1/3 cup brown sugar, eggnog, melted butter, vanilla, salt & egg whites. Spoon mixture into prepared casserole dish. Combine the 1/2 cup brown sugar & flour. Cut in the chilled 2 tbsp butter until the mixture resembles coarse crumbs. Sprinkle over the sweet potatoe mixture. Bake for 30 minutes.