Thaw the puff pastry according to the package directions. Preheat the oven to 400 degrees F.
Heat the butter and oil in a large sauté pan over medium heat. Add the onion and leek; season with salt. Cook until lightly browned, stirring occasionally, 5 to 7 minutes. Add the carrot, celery, and butternut squash; add a little salt and pepper, cook for another 5 minutes, stirring. Add the chard and garlic to the pan, stirring until the chard starts to wilt.
When the chard is wilted, add the wine to the pan and turn the heat to high. Once it comes to a boil, turn the heat down and simmer until the wine is nearly cooked off. Add the flour and cook, stirring for 1 to 2 minutes. Add the stock, turkey, rosemary, thyme and celery leaves. Simmer until the turkey is heated through and the liquid has thickened.
Off the heat, add the lemon zest, yogurt and parmesan cheese. Stir to combine and check for seasonings, adding more salt and pepper to taste.
Roll out the puff pastry on a floured surface so that it’s large enough to cover and wrap around all your ramekins; cut to size and poke each piece a few times with a fork. Ladle the filling into the ramekins, leaving some space at the top. Cover each ramekin with a piece of puff pastry, pressing the overlap on to the ramekin. Brush the tops with egg white and sprinkle with the extra parmesan and herbs.
Place the ramekins on a baking sheet and bake until the tops are golden brown, 20-25 minutes, depending on the size of your ramekins.