1 Season the meat: In a medium-sized bowl, season the beef with the salt, pepper, and garlic powder. Allow the meat sit for a few minutes to absorb the spices while you prep the rest of your ingredients.
2 Sear the meat: In a Dutch oven, or a pot with a heavy bottom, heat the vegetable oil over medium-high heat. While your oil is heating, add the all-purpose flour to the bowl with the seasoned meat. Toss the beef in the flour to coat it completely.
Once your oil is hot and you can see ripples on its surface, add half of the beef to pot. Keep the pot over medium-high heat in order to sear properly—you may want to open a window or turn on your stove vent because this can get smoky!
Sear the beef for 2 to 3 minutes, or until the beef releases easily from the pan and the bottoms look brown and crusty. Give the beef a toss with a wooden spoon and sear for an additional 2 to 3 minutes. You don’t need the meat to be cooked; you just need some good searing on the surface.
Transfer this batch of beef to a 6-quart slow cooker. Repeat the searing process with the remaining meat.
4 Cook the onion and garlic: Once all of your meat has been seared and transferred to the slow cooker, add the onion and garlic to the hot pan. Cook over medium-high heat, stirring frequently, until the onions are glossy and translucent, 3 to 4 minutes.
5 Deglaze the pan: Add 3 cups of the beef stock to the hot pot and use a stiff wooden spoon or spatula to scrape the browned bits from the bottom of the pan. Add the Dijon mustard and Worcestershire sauce to the pot and bring the mixture to a boil.
Carefully pour the mixture into the slow cooker to cover the beef chunks.
6 Cook the stroganoff: Add the bay leaf and mushrooms to the slow cooker. Give everything a stir, cover, and cook on high for 4 hours or on low for 8 hours.
7 Cook the noodles: About 15 minutes before you’re ready to eat, cook the egg noodles in a pot of boiling water. Drain and toss with a little melted butter or olive oil to keep them from sticking. Cover to keep warm until ready to serve.
Alternatively, you can cook the dry noodles directly in the slow cooker—stir them in about 15 minutes before you’re ready to serve and let them cook along with the sauce. (Just note that the noodles can quickly overcook and become mushy, so plan on serving the stroganoff as soon as the noodles are ready.)
8 Finish the stroganoff: Warm 1 cup of beef broth in the microwave for 2 minutes. In a small mixing bowl, gradually add the warmed beef broth to the sour cream, stirring constantly to temper the cream and keep it from curdling. Add this mixture to the slow cooker.
9 Garnish with herbs. Prior to serving, remove the bay leaf and stir in the chopped dill and parsley. Serve over noodles along with crusty bread and a green salad.