Blot meat dry with paper towels and season generously with salt and pepper. In a large skillet, heat oil over high heat until just smoking. Add half of the meat and cook until browned all over, flipping occasionally, 6 to 8 minutes. Transfer seared meat and remaining unseared meat to a slow cooker and stir in onion, garlic, broth, porcini mushrooms, Worcestershire, mustard, vinegar, sherry, bay leaves, ½ teaspoon salt, and ½ teaspoon pepper until well combined . Cover and cook on low until meat if fall-apart-tender, 8 to 10 hours.
Once meat is cooked, use a slotted spoon to transfer to a bowl. Use 2 forks to shred meat into chunks, removing and discarding any fatty parts. Season to taste with salt and pepper if needed. Cover to keep warm.
Pour the remaining liquid in the slow cooker into a medium saucepan over medium-high heat and bring to a simmer. Slowly whisk in flour, taking care there are no lumps. Whisk in sour cream and simmer until the sauce thickens, 3 to 4 minutes. Season to taste with salt and pepper.
In a large saucepot, bring water to a boil over high heat. Add noodles and cook until tender according to package directions. Drain and divide into individual serving bowls. Top with meat and spoon finished sauce on top. Garnish with parsley and serve.
