Ingredients
2 pounds boneless, skinless chicken breasts (about 4 medium pieces)
3 large sweet onions (such as Vidalia), thinly sliced
1/2 cup (1 stick / 113 g) unsalted butter, melted
Directions
Preheat your oven to 325°F (165°C). Lightly grease a 9×13-inch glass casserole dish so the chicken doesn’t stick.
Trim any excess fat from the chicken breasts and pat them dry with paper towels. This helps them brown slightly and keeps the texture tender instead of watery.
Lay the chicken breasts in a single layer in the prepared glass casserole dish, leaving a little space between each piece so the onions and butter can flow around them.
Peel the sweet onions and slice them into thin half-moons or rings, about 1/4 inch thick. Spread the sliced onions evenly over and around the chicken, completely covering the tops of the breasts with a generous blanket of onions.
Pour the melted butter slowly and evenly over the onions and chicken, making sure the surface is well coated. Gently tilt the dish once or twice so some butter runs underneath the chicken, helping it stay moist as it bakes.
Cover the casserole dish tightly with foil. Bake at 325°F (165°C) for 45 minutes to let the chicken gently poach in the buttery onion juices.
After 45 minutes, carefully remove the foil (watch for hot steam). Return the uncovered dish to the oven and continue baking for another 25–35 minutes, or until the onions are very soft and caramelized around the edges and the chicken is cooked through. The internal temperature of the thickest part of the chicken should reach 165°F (74°C).
Once done, let the chicken rest in the hot pan juices for 5–10 minutes. This brief rest allows the fibers in the meat to relax so the chicken stays juicy and truly “melts in your mouth.” Spoon plenty of the buttery sweet onions and sauce over each piece when serving.