These steak and mushroom pies are great for "cold-weather entertaining." It does require you to marinate the meat for a few hours and prepare the pastry beforehand, but when you see the "handsome, golden brown pies," you'll be reminded why this dish is so great.
Tuck Shop shared some tips. "To serve the pies outside of their pans (the way they do at Tuck Shop), cool the cooked pies in the pans for 30 minutes. Working close to a baking sheet, put one hand on top of a pie, and invert and slide the pie out of the pan onto your hand. Carefully transfer the pie, right-side up, onto the bak¬ing sheet. Return the pie to the oven and bake to reheat, about 10 minutes."
Make the filling: Combine the steak and stout in a medium bowl. Mix well, cover, and refrigerate for 2 to 4 hours.
Strain the steak in a sieve over a bowl, reserving the stout. Pat the steak dry with paper towels. Season the beef with 1 1/2 tsp of salt and 1/2 tsp of pepper. Heat 2 tbsp of the oil in a large Dutch oven over medium-high heat.
In three batches, add the beef to the saucepan and cook it for about 3 minutes, turning occasionally to brown lightly on all sides, adding more oil as needed. Adjust the heat as needed to keep the pan juices from burning. Transfer the browned beef to a bowl.
Add 2 more tbsp. of the oil to the Dutch oven and reduce the heat to medium. Add the onion and garlic and cook, stirring often, until softened, about 3 minutes. Add the reserved stout and bring it to a simmer, scraping up the browned bits in the pan with a wooden spoon.
Return the beef to the Dutch oven and add the rosemary. Add enough water (about 4 cups) to cover the beef by 1 inch and bring it to a simmer.
Reduce the heat to medium-low and cover. Simmer until the beef is tender, about 1 1/4 hours.
Strain the meat mixture through a wire sieve into a bowl, reserving the cooking liquid and beef separately. Discard the rosemary. Measure and reserve 3 1/4 cups of the cooking liquid, and discard the rest. Let it stand for 5 minutes, then skim off the fat from the surface of the liquid.
Meanwhile, heat the remaining 2 tablespoons oil in a large skillet over medium-high heat. Cut the mushrooms into quarters. Add the mush¬rooms to the skillet and cook, stirring occasionally, until they are lightly browned, about 8 minutes. Remove them from the heat.
Return the empty Dutch oven to medium heat. Add the butter and let it melt. Whisk in the flour and let it bubble for 1 minute. Gradually whisk in the reserved cooking liquid and bring it to a simmer. The gravy will be quite thick. Add the beef and onion mixture, mushrooms, peppercorns, and horseradish and stir. Simmer for 10 minutes to blend the flavors.
Transfer the filling to a large bowl and let it cool. Cover and refrigerate until it is chilled, at least 3 hours. (To speed cooling, place the bowl in a larger bowl of well-iced water, and let stand, stirring occasionally, until it is chilled, about 45 minutes.)
The filling must be chilled when used, or it will melt the raw pastry dough and the baked pie won’t be crisp.
Meanwhile, make the pastry: Mix the flour and sea salt together in the bowl of a heavy-duty standing mixer. Add the butter and toss with your hands to coat the butter with flour. Place the bowl on the mixer and fit the mixer with the paddle attachment.
Mix on low speed until the mixture resembles coarse crumbs with some pea-size pieces of butter. Pour in the water and mix until the dough clumps together. If the dough seems too dry, add more water, 1 tbsp at a time.
Gather up the dough in the bowl. Divide it into six equal portions (if you have a scale, they will weigh about 5.35 ounces/150 g each).
Wrap each in plastic wrap and refrigerate them for at least 30 minutes or up to 2 hours. (The dough can be made up to 2 days ahead. If the dough is chilled hard, let it stand at room temperature for 10 minutes before rolling it out.)
Working with one portion of the dough at a time, cut off one-third of the dough and set it aside for the top crust. Roll out the remaining dough on a floured work surface into an 8-inch round.
Fit the dough into a potpie pan, being sure it fits snugly into the corners and letting the excess dough hang over the edges of the pan. Fill it with one-sixth of the chilled filling. Lightly brush the edges of the dough in the pan with water.
Roll out the reserved piece of dough into a 6-inch round. Center the dough over the filling and press the top and bot¬tom crusts together. Using a paring knife, trim the excess dough at the edge of the pan. Using a fork, press around the edge of the crust to seal it. Pierce the top crust with the tip of a knife to allow steam to escape. Transfer the potpie to the refrigerator. Repeat with the remaining dough and filling. Refrigerate until the dough is chilled, about 30 minutes and up to 2 hours.
Preheat the oven to 400 degrees.
Whisk the egg and milk together in a small bowl until well com¬bined. Arrange the potpies on a large rimmed baking sheet. Brush the tops lightly with the egg mixture. Bake for 10 minutes.
Reduce the oven temperature to 350 degrees. Continue baking until the pies are golden brown, about 30 minutes more. Remove them from the oven and let them stand for 10 minutes. Serve them hot, in their pans or removed (see Note).