Tear the bread into small pieces and layer in the bottom of a greased 13x9-inch baking pan. Sprinkle onion, ham, and cheese over the bread. Beat the eggs with the milk, mustard, salt, pepper, Tabasco, and red pepper flakes until frothy. Pour over the mixture in the pan, cover tightly with aluminum foil, and refrigerate overnight.
In the morning, remove from the refrigerator and let stand at room temperature for 30 minutes. Bake in a preheated 350 degree oven until the eggs are almost set, approximately 45 minutes. Uncover and spread a layer of sour cream over the eggs, then sprinkle with Parmesan cheese and return to the oven for approximately 15 minutes.
“This is a very reliable and extremely popular breakfast dish with our guests. It makes approximately 10 to 12 servings and can be doubled or cut in half. We usually make one with ham and one vegetarian, using mushrooms, spinach, or other vegetables.” – The Tamworth Inn, Tamworth, New Hampshire