Mushroom Pot Pie

Make the crust: Combine the flour, salt, and black pepper in a medium bowl. Toss the cold butter cubes in the flour. Quickly cut the butter into the dry ingredients by pressing the cubes with your fingers, using your thumbs, middle, and index fingers to pinch the butter into smaller pieces (imagine you are snapping your fingers). When the mixture forms a coarse meal with pieces of butter resembling cornflakes, add the thyme and lemon zest and toss to combine.

Make a well in the center and pour in the cold kefir. Mix gently with your hands until the dough comes together. Don’t worry if bits of butter are still visible. Transfer to a lightly floured surface and knead briefly into a ball. Flatten into a disk and wrap tightly with plastic film. Refrigerate for at least 30 minutes and up to 2 days.

Make the filling: Cut the leek in half lengthwise and slice each piece into half-moons about ¼-inch thick. Put in a bowl and cover with cold water, swishing to remove any dirt. Let the dirt settle to the bottom of the bowl and then gently scoop the leeks from the surface using a small spider/strainer. Place the clean leeks on a paper towel or clean kitchen towel and pat dry. If the leeks are still gritty, repeat the rinsing process. When the leeks are clean, make sure to drain them well.

Use a damp towel to wipe each mushroom cap to remove any dirt. Do not rinse them, which would prevent the mushrooms from browning. Remove and discard the mushrooms stems. Slice the shiitake mushrooms thinly and cut the cremini mushrooms in quarters. Keep separately.

Heat 2 Tbsp oil on a medium pan over medium-low heat until the oil starts to shimmer. Add the leeks and a pinch of salt and cook low and slow until translucent, 8 to 10 minutes, stirring occasionally to prevent them from sticking to the bottom of the pan. Transfer to a separate bowl.

Wipe the pan clean and heat another 2 Tbsp oil over medium-high heat. Working in batches, sauté the shiitake mushrooms until they start to brown, 3 to 4 minutes, adding more oil if necessary. Be careful not to overcrowd the pan so the mushrooms brown properly. Add a pinch of salt to all mushrooms at the end of sauteing (adding at the beginning will release liquid and they won’t brown as well).

Transfer the sautéed mushrooms to the bowl with the cooked leeks. Wipe the pan clean with paper towels, heat another 2 to 3 Tbsp of oil over medium-high heat, and brown the cremini mushrooms just like you did with the shiitake. Transfer to the bowl with the leeks and shiitake mushrooms.

In a small bowl, combine 1 cup of mushroom stock with the miso using a fork or whisk to break it down. Set aside.

Wipe the pan clean one more time and add 3 Tbsp oil over low heat. Working quickly and stirring continuously, add the flour to form a paste, 2 to 3 minutes. Add the miso and stock mixture and whisk vigorously to dissolve any lumps. As the liquid begins to thicken, add 2 cups stock, the thyme sprig, and bay leaf and continue to simmer over medium heat until the liquid forms a light gravy that coats the back of a spoon, about 8 minutes.

Add the cooked leeks and mushrooms and let simmer for 2 minutes, stirring occasionally to prevent the filling from sticking to the bottom of the pan. If the filling seems too thick, stir in ½ to 1 cup of additional stock. Season to taste with salt and black pepper. Remove from heat, pour in a pie pan, and let it cool completely at room temperature. Remove thyme sprig and bay leaf.

Place an oven rack in the middle position and heat the oven to 400˚F/205˚C.

Assemble the pie: Remove the dough from the refrigerator and roll out on a lightly floured surface, forming a 12- to 13-in circle (30 to 33 cm), 1/4-in (6 mm) thick. Pick up the dough by rolling it onto the rolling pin and lay it into the pie pan. Gently press the dough on top of the filling. Trim the excess dough with kitchen scissors, leaving 1½ in of the excess dough hanging from the edge of the pie pan. Gather the dough to form a border along the edge of the pan. Crimp the border to secure to the edge of the pie pan, or if you prefer press gently with a fork creating a pattern along the edge. With a paring knife, cut 4 slits in the crust to let steam escape while baking. Brush the top crust with the beaten egg.

Place the pie pan on a rimmed baking sheet to catch any drips and bake for 25 minutes. Then rotate the baking sheet and bake for 20 to 25 minutes more (for a total baking time of 45 to 50 minutes) until the crust is a rich golden brown and the filling is bubbling through the slits. Rotating the sheet halfway through the baking process will ensure that the pie bakes evenly. Let cool for 15 minutes before serving.