1cupplain whole milk Greek yogurtdo not use nonfat or it will curdle
8ounceswhole wheat egg noodlespenne, rotini, or similar noodles work well also
Fresh parsley or thymeoptional for serving
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.
Store leftovers in the refrigerator for up to 2 days. For longer storage (up to 4 days) store the stroganoff sauce and pasta separately.
To make with ground beef instead of sirloin: In a large skillet over medium, heat 1 tablespoon oil. Add the ground beef and sprinkle with the seasonings. Cook, breaking apart the ground beef and stirring to evenly incorporate the spices, until cooked through. Drain off any excess grease and discard. Transfer the ground beef to the crock pot and proceed with step 2.
To make on the stovetop: Toss the steak strips and seasonings together in a large bowl. Heat 1 tablespoon oil in a large, deep skillet or Dutch oven over medium-high heat. Add the steak strips in a single layer and cook until brown on both sides. (Do this in multiple batches if all your steak strips can't fit.) Remove to a plate and set aside. Add another tablespoon oil to the same skillet and add the mushrooms. Cook for a 3 to 5 minutes, or until browned. Add the steak back to the skillet along with 1 cup beef broth, Worcestershire, and Dijon. Cover, reduce the heat to medium low, and simmer for 10 to 15 minutes. (Prepare your noodles while the stroganoff is cooking.) Stir together the cornstarch and remaining 1/2 cup broth to create a slurry and add to the skillet. Stir and let cook until thickened, and then stir in the Greek yogurt. Heat through and serve over prepared noodles.