For the mushroom topping:
3 tablespoons butter
1 pound mixed mushrooms, such as crimini, thinly sliced, and hen-of-the-woods/maitake, pulled into thin pieces
1 large shallot, finely chopped
2 large cloves garlic, chopped
2 tablespoons fresh thyme, chopped, or 2 teaspoons dried
Salt and pepper
2 tablespoons flour
About ¼ cup sherry or white wine
1 cup half-and-half or whole milk
For the cheese blend:
1½ cups shredded brick mozzarella
1½ cups shredded Gruyere
1 loaf French bread
Finely chopped fresh parsley
1 tablespoon fresh thyme
Melt butter in nonstick skillet over medium to medium-high heat. Add mushrooms and brown well, then add shallots, garlic and thyme, salt and pepper, stir 2 minutes, stir in flour and then add the sherry or wine and let it absorb. Add half-and-half or milk and thicken, then remove from heat.
For the blend, combine cheeses in bowl.
To serve, preheat oven to 400˚F with rack 1 above center. Line a baking sheet with parchment paper. Arrange the 4 planks of French bread and lightly toast 4 to 5 minutes. Top evenly with mushrooms and cheese, then bake 12 to 15 minutes more to brown and bubbly and top with parsley and thyme.