Preheat the oven to 425° F. Season the chicken with salt and pepper.Melt together the butter and onions in a large oven-safe skillet over medium-high heat. Cook, stirring occasionally, until softened, about 10 minutes. At this point, you'll want to slowly add the apple cider, 1/4 cup at a time, until the cider cooks into the onions. Add the garlic, mushrooms, thyme, and sage. Cook another 3-4 minutes. Add the chicken and season with salt and pepper. Continue to cook for another 10 minutes until the onions are deeply caramelized. Add the the wine and broth. Increase the heat to high and bring to a low boil. Simmer for 10 minutes, until the sauce has reduced. Stir in the cream.Arrange the bread on a baking sheet and toast for 10 minutes, until very dry. Place the bread on/around the chicken. Top evenly with cheese. Bake for 5-10 minutes, until the cheese is melted. Top with thyme. Serve and enjoy! YUM!