Ingredients:
4 tablespoonsextra-virgin olive oil, divided
2 large or 3 medium leeks, tough outer layers removed, halved lengthwise, washed very well and white and pale green parts sliced thinly
1 poundmixed mushrooms, sliced (a mixture of shiitake, cremini, oyster, maitake, and trumpet would be excellent)
Kosher salt and freshly ground black pepper, to taste
1 pinchred pepper flakes
2 tablespoonsvegan butter (substitute more olive oil if you don’t like or have this)
2 cloves garlic, finely chopped
5 to 6 sprigs thyme, leaves only
5 5 to 6 sage leaves, thinly sliced into ribbons
1 tablespoonwhite miso
2 tablespoonsall-purpose flour
1/4 cupdry white wine, cider vinegar, or apple cider (hard or not)
1 3/4 cupsvegetable stock or plain unsweetened oat milk (for a richer texture), at room temperature
2 tablespoonsnutritional yeast (optional)
1 sheet vegan puff pastry (like Pepperidge Farm), thawed
Aquafaba or melted vegan butter, for brushing
Directions:
Heat the oven to 400°F.
In a large skillet over medium-high heat, add the olive oil and heat until shimmering. Add the leeks and saute until softened and translucent, 6 to 8 minutes. Pour in the second two tablespoons of olive oil and heat momentarily. Add the mushrooms to the pan, plus a big pinch of salt and a few cranks of black pepper and red chile flakes, and cook until the mushrooms have expelled most of their liquid and begin to brown, 6 to 8 more minutes. Transfer the mushrooms and leeks to a separate container (like the 2-quart baking dish you’ll eventually use to bake the pie) and set aside.
To the same skillet, over medium heat, add the vegan butter and heat until fully melted. Add the garlic, thyme, and sage leaves and cook until fragrant and slightly browned, 1 to 2 minutes. Add the white miso and stir, cooking for another 30 seconds or so until it’s incorporated in the garlic and herb mixture. Next, add the all-purpose flour and cook for 1 to 2 minutes, stirring occasionally, until the flour is coated in the fat and no dry pockets are visible.
Carefully pour in the dry white wine, scraping the bottom of the pan and stirring the mixture so the liquid incorporates into the roux. Then, slowly add the vegetable stock or oat milk to the pan, stirring vigorously until no floury lumps remain. Bring the mixture to a rollicking simmer, then lower the heat and add the reserved mushrooms and leeks, plus the nutritional yeast, if using. Stir to combine and cook for another 3 or so minutes, letting the mixture thicken—you want it to be roughly the consistency of chowder, but not much thicker than that, as it’ll continue to firm up in the oven (add more liquid if yours evaporated too quickly). Taste and adjust seasoning as needed with more salt, pepper, or even sage or thyme leaves.
Transfer mushroom-leek mixture to a medium (2-quart) baking dish (a 7×10 or 7×11-incher should fit the mixture and work nicely with the size of the puff pastry sheet; a 10-inch cast-iron skillet also works), and smooth out into an even layer.
Roll the puff pastry so there’s a 1/4-inch overhang on all sides. Gently place puff pastry sheet over the baking dish, draping it so it hangs over the edges of the pan. Pinch the overhang onto the edge of the pan and add a few slits down the middle of the pie to let out steam and allow the pastry to fully puff up. Brush the top with aquafaba or melted vegan butter to encourage browning.
Place the baking dish in the oven and bake for 15 minutes; then lower the heat to 375°F and bake for another 25 to 30 minutes, until the pastry has puffed up fully (it should be considerably taller than when raw). If you see the top getting too dark too quickly, you can tent some foil over the dish for the second part of the bake. Let cool slightly before eating.