To make the casserole: In a large bowl or resealable plastic bag, combine the flour, salt, and pepper. Dredge the beef in the flour mixture and set aside. Lightly grease a 3-quart casserole dish.
In a large skillet over medium heat, heat the oil. Add the onion and garlic and cook for 2 to 3 minutes, or until soft but not browned. Add the beef and cook for 3 to 5 minutes, or until browned on all sides. Add the carrots and celery and stir to coat. Stir in the ale, stock or broth, tomato purée, Worcestershire sauce, and thyme. Bring to a boil, then reduce heat to low, cover, and simmer for 30 minutes, or until the meat and vegetables are tender and the sauce starts to thicken. Transfer the mixture to the prepared dish.
To make the cobbler: Preheat the oven to 350ºF. Sift the flour and mustard into a food processor. Season with salt and pepper. Add the butter, and pulse 4 to 5 times, or until the mixture resembles coarse crumbs. Add the cheese, Tabasco, and 1/2 cup water. Process for 8 to 10 seconds, or until a soft dough forms. Add more water, if necessary. Transfer the dough to a floured surface. Roll it out to 1/2-inch thickness. With a 3-inch round cookie cutter, cut out rounds. Arrange the rounds on top of the meat mixture, overlapping in a decorative pattern. Brush the tops of the cobbler with the milk. Bake for 30 to 35 minutes, or until the top is golden and the mixture is heated through. Remove from the oven and serve immediately.