Heat oil in a 12-inch skillet over medium heat until it shimmers. Add mushrooms, onions, and 1/4 tsp salt.
Cover and cook for 5 mins until vegetables soften. Uncover and cook for 5-7 mins until dry and lightly browned.
Stir in flour, tomato paste, garlic, porcini mushrooms, and thyme; cook until fragrant, about 1 min.
Gradually stir in wine and 1/2 cup chicken broth, scraping up any browned bits, then transfer to the slow cooker.
Add remaining 1 cup broth, soy sauce, and bay leaves to the slow cooker.
Season beef with salt and pepper; add to the slow cooker. Cover and cook on low for 8-9 hours or high for 5-6 hours until beef is tender.
Remove bay leaves and skim fat from the surface. Whisk together 1/2 cup sauce, sour cream, mustard, and dill. Stir this back into the slow cooker.
Adjust seasoning with salt and pepper. Serve immediately over egg noodles.