Step 1: Pat chicken dry with paper towels. In a shallow dish, combine flour, 1 tsp salt, and 0.5 tsp pepper. Dredge chicken pieces lightly in the flour mixture, shaking off any excess.
Step 2: Melt butter in a large Dutch oven or oven-safe pot over medium-high heat. Add chicken and sear for 3-5 minutes per side until golden brown. Remove chicken from pot and set aside.
Step 3: Reduce heat to medium. Add sliced onions to the pot and cook, stirring occasionally, for 10-15 minutes until softened and deeply caramelized. This step is crucial for flavor.
Step 4: Pour in apple cider, scraping up any browned bits from the bottom of the pot with a wooden spoon. Bring to a simmer.
Step 5: Add mushrooms, minced garlic, and fresh thyme. Cook for 2-3 minutes, stirring, until fragrant.
Step 6: Return seared chicken to the pot, nestling it into the sauce. Pour in chicken broth or white wine, ensuring the chicken is mostly submerged. Add fresh sage leaves, if using.
Step 7: Cover the pot and transfer to a preheated oven at 350°F (175°C). Braise for 45-60 minutes, or until chicken is fork-tender and cooked through (internal temperature 165°F/74°C).
Step 8: Carefully remove the pot from the oven. Taste the sauce and adjust seasoning if needed. Serve hot with your favorite side dishes.