ingredients

cooking

1. Heat the oil in a large pot or Dutch oven over medium-high heat. Season the beef generously with Kosher salt and pepper on all sides, then add it to the skillet. Brown for a few minutes on each side. 
2. Add the onion, carrots, and celery, and cook until starting to soften, stirring occasionally, 3-4 minutes. 
3. If there's no or very little oil left in the pan, add a bit more. Stir in the potatoes and mushrooms and cook an additional 3-4 minutes. Stir in the garlic and sauté until fragrant, about 1 minute. 
4. Add the rosemary and thyme to the pot. Pour in the Guinness, scraping up any browned bits from the bottom of the pan. Add the stock and give everything a good stir. 
5. Turn the heat to low, cover, and allow the mixture to gently simmer for 1-1.5 hours, or until the beef is fork tender. Taste and season with additional salt and pepper if needed. 
6. Stir the cornstarch mixture into the pot, and bring to a gentle boil, allowing the mixture to thicken for several minutes. Remove from heat. 
7. Preheat the oven to 400 degrees. Remove the puff pastry from the packaging and cut it to the size of your baking dish or skillet. Whisk together the egg and water, then brush it on one side of the pastry. Layer the pastry, egg side up, over the beef mixture, overlapping slightly. Put a few slashes across the top for steam to escape. Transfer to the oven and bake for 30-35 minutes or until pastry is very golden and puffed. Serve immediately.
   

Notes 

• If you don't have or can't find stew beef, buy a chuck roast and cut it into bite-size chunks. The Guinness can be substituted with additional beef broth, another stout beer, or red wine if you prefer. 
• You can use any large, shallow pan to bake the pie. If needed, transfer the filling to a 9 x 13-inch pan, deep dish pie pan, or even individual ramekins. 
• Make sure the mixture is thickened enough. It should be a little thicker than gravy. You can always add additional cornstarch slurry, ½ tablespoon at a time if needed. 
• Keep the pastry cold. The puff pastry should be thawed, but kept chilled. I do not recommend microwaving the puff pastry to thaw it, unless you have time to stick it back in the fridge for awhile after. You can prep the pastry by cutting it and adding the egg wash at any point while the filling is cooking, just make sure to cover it and place it back in the fridge until you’re ready to top the pie. 
• Measure the puff pastry with the pan you'll be using. To make it easier to measure the pastry, place whatever pan you're using on top of it and cut it to size before starting the recipe. 
• Use your puff pastry scraps! Bake any leftover puff pastry scraps on a separate pan. You can even sprinkle them with everything bagel seasoning or cinnamon sugar, similar to a pie crust cookie!