1. In a food processor, pulse the flour and salt until combined. Add the cold butter and pulse until the mixture resembles coarse crumbs. Gradually add the ice water and pulse until the dough just begins to come together. Divide the dough into two discs, wrap in plastic, and refrigerate for at least 30 minutes.

2. In a large Dutch oven or heavy-bottomed pot, heat the beef tallow over medium-high heat. Add the beef and brown on all sides, about 5 minutes. Remove the beef from the pot and set aside.

3. Add the onion, carrots, celery, and garlic to the pot and cook until softened, about 5 minutes. Sprinkle in the 1/4 cup of flour and stir to coat the vegetables.

4. Slowly pour in the ale, scraping up any browned bits from the bottom of the pot. Stir in the beef broth, Worcestershire sauce, bay leaf, and thyme. Return the beef to the pot and bring the mixture to a simmer.

5. Reduce the heat to low and let the filling simmer for 45 minutes to 1 hour, or until the beef is very tender. Season with salt and pepper to taste.

6. Preheat your oven to 375°F (190°C).

7. On a lightly floured surface, roll out one of the dough discs to fit a 9-inch pie dish. Transfer the dough to the dish and pour the beef filling into the crust.

8. Roll out the remaining dough disc and place it over the filling. Crimp the edges to seal and cut a few slits in the top to allow steam to escape.

9. Bake the pot pie for 30-35 minutes, or until the crust is golden brown. Let cool for 10 minutes before serving.