1/4 cup plus 3 tablespoons butter, melted, divided
18 slices day-old French bread (3/4 inch thick)
1/2 cup stone-ground mustard
1-1/2 cups cubed fully cooked ham
1 cup sliced fresh mushrooms
2 garlic cloves, minced
1/4 cup chopped green onions
2 cups shredded Swiss cheese
8 large eggs
4 cups heavy whipping cream
1/2 teaspoon salt
1/2 teaspoon pepper
2 tablespoons minced fresh parsley
Warm maple syrup, optional
Pour 1/4 cup melted butter into a 13x9-in. baking dish; set aside. Spread both sides of bread slices with mustard. Arrange 9 slices in baking dish.
In a large skillet, saute the ham, mushrooms and garlic in remaining butter until mushrooms are tender. Add the onions; cook until crisp-tender, about 1 minute longer. Spoon ham mixture over bread; sprinkle with cheese. Arrange remaining bread slices on top. In a large bowl, beat the eggs, cream, salt and pepper. Stir in parsley; pour over bread.
Place dish in a larger roasting pan; add 1 in. hot water to larger pan. Bake at 325° until a knife inserted in the center comes out clean, 50-60 minutes. Let stand for 5 minutes before serving. Drizzle with maple syrup if desired.