Preheat oven to 180 C. Grease a 9 x 13 inch baking dish or use a non stick dish. For the thighs, if cutting them from quarters, they are generally larger. Not recommended to use thighs and legs as the cooking time will be different for each.
Pour the soup into a medium bowl. Fill the empty can with milk, and add to the bowl along with the parsley and onion powder. Mix well, season with salt and pepper if desired.
Place bread crumbs in a shallow dish or bowl; dip chicken thighs in soup mixture, then in crumbs, coat well with the crumbs, and place coated pieces in the baking dish.
Drizzle with melted butter and bake in preheated oven until chicken is nicely browned and cooked through (juices run clear), about 45 minutes. NOTE, check at 45 minutes, for larger thighs, you may need to increase time to 60 or 75 minutes. This a 9x13 baking dish, that is actually 2 thighs in the back row, and 3 in the front.
Meanwhile, place remaining soup mixture in a small saucepan and whisk in the corn starch and fresh mushrooms if you are using them. Cook over medium heat, stirring occasionally, until mixture comes to a boil, then reduce heat and simmer for a minute or two until sauce thickens. Use this as a sauce/gravy when chicken is done.
When it comes out of the oven, let it rest for a few minutes before serving. The liquid you see is butter and chicken fat (flavor). I made these with skin on thighs, recipe adjusted to skin off and excess fat removed.
Serve with mashed potatoes, boiled potatoes, rice, or pasta. Recommended side dish is steamed fresh broccoli or yards beans. I served mine over rice, not a great photo but I spooned the sauce over the chicken that was on a bed of rice.