Ingredients:
Mornay sauce
1 1/2 tablespoons butter
1 1/2 tablespoons all purpose flour
1 1/2 cups whole milk
1 bay leaf
1/2 cup finely grated Parmesan cheese
Pinch of freshly grated nutmeg
Hot pepper sauce
Sandwiches
1 8-ounce package crimini (baby bella) or button mushrooms, trimmed
7 tablespoons butter, room temperature, divided
2 tablespoons minced shallot
12 1/3-inch-thick slices egg bread
6 thin ham slices
12 ounces Gruyère cheese; 9 ounces thinly sliced, 3 ounces grated
2 tablespoons grated Parmesan cheese
Fresh tarragon leaves (optional)
Directions:
Mornay sauce
Melt butter in heavy medium saucepan over medium heat. Add flour; stir until pale golden, about 2 minutes. Whisk in milk. Add bay leaf. Increase heat to medium-high; whisk until mixture begins to boil. Reduce heat to medium; stir until sauce coats back of spoon, about 5 minutes. Remove from heat. Add cheese and nutmeg. Season with hot sauce, salt, and pepper.
Sandwiches
Place mushrooms in processor. Using on/off turns, process until finely chopped. Melt 3 tablespoons butter in large skillet over medium-high heat. Add mushrooms and shallot; stir until mushrooms are browned and dry, about 8 minutes. Transfer to plate to cool.
Preheat broiler. Spread remaining butter over 1 side of bread slices. Place bread, buttered side up, on rimmed baking sheet. Broil until golden, watching closely and rotating sheet halfway through broiling, about 3 minutes. Cool bread. Preheat oven to 450°F. Turn 6 bread slices over; top with ham and sliced cheese. Top with remaining bread slices, broiled side up. Press to compress. Spread about 2 tablespoons sauce over sandwiches, leaving 1/3-inch plain border. Divide mushroom mixture atop sauce. Sprinkle with grated Gruyère and Parmesan.
Bake sandwiches until cheese inside melts and cheese on top turns golden, about 10 minutes. Top with tarragon, if desired.
