Buttermilk roux enrobes meaty mushrooms and velvety onions, folded inside flaky crumb. The best thing to warm chilly hands on a blustery day.
Make the dough. In a large bowl, stir together the flour, salt, and pepper. Add the butter and cut in, using a pastry blender, until pea sized bits remain. Pour vinegar into ice water and drizzle a little at a time, cutting in the liquid into the crumbly butter- flour mixture, until a dough forms. If you squeeze the dough in your hand and it holds, it is ready. Repeat drizzling and cutting in, if it is not ready. On 2 large segments of cellophane, divide the dough and pat it into 2 disks. Wrap snugly and refrigerate for at least 20 minutes, to allow the dough to mellow. Between lightly floured pieces of parchment, roll dough to 1⁄4”–1⁄8” thick, transferring to a baking sheet to chill at any point if the pastry becomes smeary or flabby. Use a bowl or teacup with a 5” diameter to trace circles with a sharp knife, re- rolling scraps as needed. Transfer pastry rounds on a baking sheet to the refrigerator. Heat butter and 1 tablespoon olive oil in a cast iron skillet over medium- high heat and sauté chanterelles, stirring occasionally. When they begin to soften, add the thyme sprigs and sauté for another few minutes. Transfer mushroom mixture to a bowl and set aside. Add the remaining tablespoon of oil into the pan and swirl to coat. Add the onion, lower heat, and cook until translucent, stirring often to prevent browning. After the onions become translucent, they will darken and caramelize as you occasionally stir to distribute them around the pan. After 20 minutes, they should be soft, darkened, and sweet. Transfer to the dish with cooked mushrooms, just after removing thyme stems. To make the roux, melt butter in a small sauté pan and heat until foaming. Add flour and whisk to incorporate. Once fully combined, add the buttermilk, a little at a time. Whisk well to incorporate, and remove from heat if bubbling or it becomes quite thick. Return to heat, add a drizzle of water, and whisk again. The roux should be thick but not paste-like. Thin further as needed. Remove from heat and fold into melted onion-chanterelle mix. When cooled to room temperature, add 2 spoonfuls of the mushroom mixture to each pastry round, on 1 side. Lightly brush water around the edge and fold the empty side over the contents, pressing the pastry edge to seal. You may crimp or fold the edge in for a decorative touch, then brush egg wash on top-facing side. Chill for at least 1 hour, or freeze for 1⁄2 hour. While pies chill, preheat oven to 425°F. Bake for 15 minutes, then rotate pan for even browning. Bake for 10 or so minutes more, until deeply golden. Transfer hand pies to a wire rack and allow to cool for at least 10 minutes before giving in to temptation.