Rinse the chicken under cold water and pat dry with paper towels.
In a large pot, heat the butter and olive oil and brown the chicken on all sides. Then remove the chicken.
Sauté the chopped bacon for 5 minutes until it starts to brown. Set the bacon aside but leave the fat in the pot.
Cook the leeks and mushrooms in the same pot until they start to soften. Then add the apple juice, chicken broth, honey, and thyme. Season with salt and pepper to taste.
Place the chicken, bacon, and leek-mushroom mixture into the slow cooker. Add the diced apples.
Cook on high for 4 hours.
Collect the cooking liquid and stir in a bit of cornstarch diluted in one tablespoon of apple juice to slightly thicken the sauce (optional).
Tip: You can thicken the sauce directly in the slow cooker or in a small saucepan.
Serve the chicken drizzled with sauce and alongside mashed potatoes.