In two batches, brown sliced mushrooms in oil over medium-high until released moisture evaporates. Transfer to a 6-quart slow cooker.
Cook onion 3 to 4 minutes and garlic 30 seconds. Add 1 1/2 cups broth, scrape pan and whisk in Dijon, Worcestershire, paprika, thyme, 1/2 teaspoon salt and pepper. Pour over mushrooms.
Season thawed trimmed thighs with remaining salt and arrange over mushroom mixture.
Cover and cook on low 4 to 5 hours or high 2 to 3 hours, beginning checks at the earliest time.
Remove each thigh when its thickest center reaches 165°F. Rest 5 minutes on a clean plate.
Whisk flour with remaining 1/2 cup cool broth. Boil with 2 cups cooking liquid in a saucepan for 2 to 3 minutes, then return to cooker.
Boil egg noodles separately according to package directions; drain and toss with optional butter.
Gradually whisk 1 cup hot sauce into sour cream. Switch off cooker and stir tempered mixture into remaining sauce without boiling.
Cut chicken into large pieces and fold into sauce. Add lemon and parsley or dill; taste and serve over noodles.
