Bring a large pot of salted water to boil for egg noodles. Cook according to package directions until al dente, drain, and toss with butter to prevent sticking.

Heat a large skillet or Dutch oven over medium-high heat. Add ground beef, breaking it up with a wooden spoon. Season with salt, pepper, paprika, and thyme. Brown for 6-8 minutes until no pink remains. Drain excess fat if needed.

Push beef to one side of the pan. Add butter to empty space. When melted, add diced onion and cook 4 minutes until softened. Add sliced mushrooms and cook 8-10 minutes until golden brown.

Stir in minced garlic and cook 30 seconds until fragrant. Sprinkle flour over the mixture and stir well to coat everything evenly.

Slowly pour in beef broth while stirring constantly. Add Worcestershire sauce and Dijon mustard. Bring to a gentle simmer.

Simmer for 5-7 minutes, stirring occasionally, until sauce thickens enough to coat the back of a spoon. Remove from heat and let cool 1 minute.

Stir in room-temperature sour cream until fully incorporated and sauce is creamy and smooth. Taste and adjust seasoning with salt and pepper.

Serve immediately over cooked egg noodles. Garnish with fresh chopped parsley.