4 cups, day-old, challah or brioche bread, cut into 1-inch cubes.
2 tablespoons olive oil
1 tablespoon unsalted butter
1 medium sweet yellow onion, peeled and diced
½ teaspoon kosher salt
½ teaspoon freshly ground black pepper
¼ teaspoon granulated sugar
½ lb. thinly-sliced good deli ham, roughly cut
6 large eggs
1½ cups milk or half ‘n half
½ teaspoon dry mustard
¼ teaspoon grated nutmeg
2 teaspoons fresh thyme leaves, minced
Salt & Pepper, to taste
1 cup shredded Gruyere or Swiss cheese
1. Spray an 8-inch baking dish (1½-2 qt) with non-stick cooking spray.
2. Spread the cubed bread in the bottom of the dish.
3. Heat oil and butter in a large skillet over medium-low heat. Add diced onion, salt, black pepper and sugar. Sauté until onions are lightly caramelized, approximately 10 minutes. Be careful not to burn the onion.
4. In a medium bowl, whisk together the eggs, milk, nutmeg, thyme, salt and pepper.
5. Spread the ham over the bread cubes, then spread the onion mixture on top of the ham. Layer on the Gruyere or Swiss cheese then pour the egg mixture over the cheese.
6. Press down gently on the top to ensure all bread cubes get soaked with the egg mixture. Cover and refrigerate overnight.
7. Before baking, warm the casserole on the counter for 15 minutes and preheat the oven to 350 degrees F.
8. Bake, uncovered, 35-40 minutes or until center is set and edges are bubbly and top begins to brown. A knife inserted in the center should come out clean.