Mix the Seasoning: Combine brown sugar, pepper, salt, garlic powder, onion powder, chili powder, and paprika in a small bowl and set aside. Measure and prep all remaining ingredients before you begin cooking.
Cut the beef into roughly one-inch cubes, trimming away large, tough pieces of fat. Marbled fat throughout the meat is fine and should stay. Season the cubes with the spice blend right before cooking, toss to coat, then sprinkle over the flour and toss again.
Sear the Beef: Heat 3 tablespoons of olive oil in a large pot or Dutch oven over medium-high heat. Working in batches so the pan isn't crowded, add the beef and sear for 30 to 40 seconds per side until browned on the outside. The center should still be red and cold. Transfer to a plate and add more oil between batches as needed.
Turn off the heat. Wipe away any truly black burned spots from the bottom of the pan but leave the brown residue (fond) in place.
Deglaze with Wine: Once the pan has cooled slightly, add the wine and return the heat to medium-high. Use a silicone spatula to scrub the bottom of the pan and dissolve the fond into the liquid. Let it reduce by half, about 3 to 5 minutes.
Add 2 tablespoons of the butter and the diced onion. Cook for 4 minutes, then add the garlic and cook for 1 more minute. By now the wine should be nearly absorbed and the onions will be soft and reddish.
Build the Broth: Return the seared beef to the pot along with the tomato paste, Worcestershire sauce, bay leaves, rosemary, ground sage, beef broth, and bouillon. Stir to combine.
Cover the pot, leaving a small gap for steam to escape, and simmer over medium-low heat for 2 hours. The liquid should bubble gently and reduce slowly.
Thicken and Finish: When the beef is tender, bring the soup to a full boil. Add the cornstarch and cold water to a small container, seal, and shake until fully combined. Slowly pour the slurry into the boiling soup in increments, stirring constantly, until the soup reaches your desired thickness.
Reduce the heat to low. Add the frozen vegetables and stir to combine. Cook for 10 minutes until heated through and just tender. Add Gravy Master if a deeper color is desired.
Remove the bay leaves and rosemary stem. Swirl in the remaining 2 tablespoons of cold butter until fully incorporated. Garnish with chopped parsley and serve immediately over mashed potatoes or alongside biscuits.
Crock Pot Method: Complete steps 1 through 6 on the stovetop. Transfer the onion and garlic mixture along with all remaining ingredients (except cornstarch mixture and frozen vegetables) to a slow cooker, using only 6 cups of broth. Cook on low for 7 1/2 to 8 hours or high for 3 1/2 to 4 hours. Turn heat to high, stir in the cornstarch slurry, and simmer for 5 minutes. Add frozen vegetables and cook for 15 more minutes. Turn off the heat, remove bay leaves and rosemary, and swirl in the cold butter.