Mushroom Croque-Monsieur

Preparation

1. For mornay sauce:

   Step 1

   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.

2. For sandwiches:

   Step 2

   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.

   Step 3

   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.

   Step 4

   Bake sandwiches until cheese inside melts and cheese on top turns golden, about 10 minutes. Top with tarragon, if desired.