Preheat the oven to 400 degrees . In a large saucepan of boiling, lightly salted water, cook the farro, undisturbed, until tender, 20 to 25 minutes; drain.
Meanwhile, in a medium skillet, fry the bacon over medium heat until crisp, 5 to 7 minutes; drain on paper towels. Crumble and reserve.
In a medium saucepan, melt the butter over medium heat. Whisk in the flour until smooth; cook until pale golden, about 2 minutes. Whisk in the milk and cook until thickened, about 5 minutes. Whisk in half of the cheese until smooth, about 3 minutes.
In a large bowl, combine the cooked farro, three-quarters of the bacon, the cheese sauce and 1/4 teaspoon each salt and pepper. Spread evenly in a greased 9-by- 13-inch baking dish; sprinkle the remaining cheese and bacon on top. Bake until the cheese is melted and golden, about 30 minutes. Let stand for 5 minutes before serving.