Mix the Panko, Parmesan, salt and pepper in a small bowl. Set aside
Bring a large pot of salted water to a boil and cook the pasta for 10 minutes. Reserve a cup of the pasta water and drain the rest.
While the pasta cooks heat a Dutch oven over medium-high heat. Add the Olive Oil, mushrooms, Thyme, 1/2 tsp Salt and the Shallots. Cook until softened and beginning to brown. Remove to a plate.
Preheat your broiler
Reduce the heat under the Dutch oven to medium. Add the Butter and Flour. Mix to form a paste. Continue stir and cook for another minute. Whisk in the Milk stirring to prevent it sticking. Simmer for 5 minutes. Whisk in the Gruyere, Fontina and Parmesan. Stir to fully incorporate
Add the Pasta, the reserved Pasta Water, cooked mushroom mixture, 3/4 tsp Salt and pepper. Fold everything together. Top with the breadcrumb mixture and drizzle with olive oil. Broil until the breadcrumbs are golden brown and the sauce is bubbling
Allow the Mac & cheese to sit for 10 minutes before serving