Preheat oven to 400F; lightly grease an 8x8 pan. Heat oil in large skillet over medium high heat; add the celery and cook 3 minutes, then add onion, salt, pepper and bay leaf and saute 7 minutes. Add the mushrooms and cook until all the veggies are tender and the mushrooms are browned, about 7-10 minutes. Add the garlic, Herbes de Provence and cook 1-2 minutes more; cool slightly.
Stir together the veggie mixture with the bread crumbs, egg, Worcestershire sauce a large portion of the Parmesan and half the cheddar in a large bowl. Spread the stuff mixture into the prepared dish. Sprinkle the remaining cheddar and the reserved 2 Tablespoons of Parmesan on top and dot on the butter.
Bake until the cheese is melted and golden brown in places on top about 15 minutes. Broil it for a couple minutes if you want it to have more color.