Position a rack in the center of the oven and preheat to 350°F. Season the chicken legs all over with salt and black pepper.

To a large, heavy pot over medium-high heat, add the oil. When hot and shimmering, working in batches of 2 legs, add the chicken skin-side down and cook, turning once, until golden brown and crisp on both sides, 10–11 minutes total, adding more oil if needed. Using tongs, transfer to a paper towel-lined plate.

Add the bacon to the pot and cook until most of the fat has rendered and the bacon is beginning to brown, about 5 minutes. Using a slotted spoon, transfer the bacon to a paper towel-lined plate. Drain off all but 1 tablespoon of fat from the pot, then turn the heat to medium. Add the onion and celery and cook, stirring occasionally, until the onion is translucent, about 5 minutes. Add the garlic and cook, stirring occasionally, until fragrant, about 2 minutes. Add the flour and cook, stirring, for 1 minute. Stir in the cider and bring to a simmer, then add the stock, thyme, and bay leaf and bring back to a simmer.

Return the chicken to the pot, skin-side up. Cover and bake until the chicken is tender and falling off the bone, about 40 minutes.

Using tongs, transfer the chicken to a platter and tent with foil, then place the pot on the stove. Add the crème fraîche, turn the heat to medium, and whisk until incorporated. Cook, stirring occasionally, until bubbling and thick enough to coat the back of a spoon, 8–10 minutes. (For a thicker, more gravy-like sauce, continue to simmer for up to 10 minutes more.) Discard the bay leaf and thyme sprigs and season with salt and black pepper.

Return the chicken to the pot skin-side up along with the bacon. Garnish with parsley and serve in the pot with lemon wedges and crusty bread on the side. (In an airtight container, leftovers will keep in the fridge for up to 4 days or in the freezer for up to 1 month.)