1. Preheat oven to 350°F (175°C).
2. In a large pot, heat olive oil over medium heat. Add beef and cook until browned.
3. Add onion and garlic, cook until softened.
4. Stir in tomato paste, Guinness, beef stock, thyme, salt, and pepper. Bring to a boil, then reduce heat and simmer for 1 hour.
5. While the filling is cooking, prepare the pastry. In a bowl, combine gluten-free flour and salt. Cut in butter until mixture resembles coarse crumbs. Add cold water and mix until dough forms.
6. Roll out dough and line a pie dish with half of it. Fill with beef mixture, then cover with remaining dough. Seal edges and cut slits in the top.
7. Bake in preheated oven for 45 minutes, until crust is golden brown.