Pat the beef dry with a paper towel and season it generously with salt and pepper. 

Heat a large heavy-bottomed skillet over medium-high heat.

Add the olive oil and sear the meat for 1-2 minutes per side. You want to develop a good crust on the meat, not cook it all the way through. Make sure not to overcrowd the pan– feel free to cook the meat in batches if you need to. 

Once browned, transfer the beef to the slow cooker.

Top the beef with the mushrooms, onion, garlic, and thyme. 

Finally, pour over the beef broth and Worcestershire sauce.

Cover the slow cooker and cook on high for 4 hours or low for 6 hours. 

When the beef is easily shreddable, remove it from the slow cooker and shred it into large chunks. 

Remove all but ½ cup of beef stock and add the sour cream to the slow cooker. Stir it into the sauce. 

Add the beef back to the slow cooker and toss it with the sauce. 

Serve the beef stroganoff over egg noodles or mashed potatoes and garnish with fresh parsley or thyme. 

Store any leftover beef stroganoff in an airtight container in the fridge for up to three days.