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Export 12 ingredients for grocery delivery
Grease the bottom of a 6-quart or larger slow cooker with nonstick spray. Add the sirloin and sprinkle with salt, dill, black pepper, garlic powder, and onion powder. Stir to coat the meat.
Add the mushrooms, 1 cup beef broth, Worcestershire, and Dijon. Cover and cook on high for 2 to 3 hours or on low for 5 to 7 hours, until the beef is cooked through and tender. (If you prefer firmer mushrooms, wait to add them until about halfway through the cook time.)
Stir the cornstarch together with the remaining 1/2 cup broth to create a slurry. Stir the mixture into the slow cooker. Cover and cook on high for 20 minutes, and then stir in the Greek yogurt. Re-cover and cook on high for an additional 10 minutes.
While the stroganoff finishes cooking, cook the noodles according to package instructions. Stir into the slow cooker or pile separately into bowls and ladle the stroganoff over the top. Serve immediately, topped with fresh thyme or parsley as desired.