Heat the olive oil in a large stock pot over medium heat. In a medium-size bowl, toss the beef cubes with ¾ teaspoon salt and ½ teaspoon pepper. Carefully arrange the beef cubes in the hot oil and sear until brown on all sides, about 5-7 minutes total. Remove the beef from the pot.
Place the butter in the pot and stir to melt. Add the onion, carrot, celery, and mushrooms and sauté for about 5 minutes until softened. Add the garlic and cook for 1 more minute. Place the tomato paste, worcestershire, thyme, rosemary, and the remaining ½ teaspoon salt and ¼ teaspoon pepper in the pot. Stir and toast for 1 minute.
Deglaze the pot with the gluten-free stout and pour in the beef stock. Add the beef cubes back to the pan along with 2 bay leaves. Bring the pot to a boil on high heat then reduce to low, cover, and allow to simmer for 2 hours and 15 minutes until the beef is soft. Stir occasionally. Make the shortcrust pastry below while the filling cooks.
After 2 hours and 15 minutes, the beef should be cooked and mostly soft. In a small bowl, mix together the cornstarch and water and pour into the pot. Stir and cook uncovered for an additional 15 minutes. The filling will become quite thick. Discard the bay leaves. Turn off the heat and set the pot aside to cool for at least 1 hour, or cover and refrigerate overnight.