Put an oven rack in the center of the oven. Preheat the oven to 400 degrees F. Butter a 9 by 13 by 2-inch glass baking dish. Set aside.
Farro: In a large stockpot, bring the farro, water and salt to a boil over medium-high heat. Reduce the heat, cover the pot, and simmer until the farro is tender, about 25 to 30 minutes. Drain in a colander.
Filling: In a large bowl mix together the cheeses, milk, herbes de Provence, salt, and pepper. Add the cooked farro and stir until coated. Pour the mixture into the prepared baking dish.
Topping: Arrange the bread pieces on top of the farro mixture and drizzle liberally with olive oil.
Bake for 15 minutes until the topping is golden. Cool for 5 minutes and serve.