To make the chuck roast (skip if using leftovers):

1. Preheat oven to 350°F.
2. Pat the chuck roast dry and season evenly with salt, pepper, and rosemary on all sides.
3. Heat a heavy duty skillet over high heat. Sear the roast on all sides, turning as needed with tongs.
4. Transfer to a Dutch oven and add onion, celery, carrots, and garlic along with enough water to come halfway up the roast.
5. Cover and roast for 2½ to 3 hours until fork-tender.
6. Remove roast and shred the meat. Reserve all liquid and vegetables — these become the base of your stroganoff.

To make the stroganoff:

1. In a medium stockpot, combine the reserved roast liquid with beef base and tomato paste. Add water if needed to make 1 quart. As it heats, use a fork to smash the cooked vegetables into the broth. Bring to a gentle boil.
2. While the broth heats, melt butter in a sauté pan over medium-high heat. Add mushrooms and cook for 5 to 7 minutes until browned. Add flour and stir to combine.
3. Add egg noodles to the simmering broth and cook until tender, about 8 minutes.
4. Stir in the mushroom mixture until the sauce reaches a gravy-like consistency. If it's too thick, add ¼ cup water or milk.
5. Add shredded beef and stir in sour cream. Season with salt and pepper to taste. Serve warm.