Sauté Vegetables
Melt butter in a large pot over medium heat. Add diced onions, green bell peppers, and mushrooms. Cook until onions are translucent, about 5-7 minutes. This creates the aromatic base of your soup and softens the vegetables to the perfect texture.
Add Meat and Garlic
Stir in chopped roast beef and minced garlic. Cook for 2-3 minutes until the garlic is fragrant. This step helps to release the flavors of the garlic and slightly warm the beef without overcooking it.
Create a Roux
Add flour to the pot, stir well, and cook for 3 minutes. This creates a roux that will help thicken your soup and give it a velvety texture. Be sure to cook the flour long enough to remove any raw taste.
Add Liquids and Seasonings
Gradually add beef broth while stirring continuously to prevent lumps. Add half and half, Worcestershire sauce, salt, and pepper. Stirring constantly during this step ensures a smooth, creamy soup base.
Simmer the Soup
Bring the soup to a boil, then reduce heat and simmer for 10 minutes, stirring occasionally. This allows the flavors to meld together and the soup to begin thickening naturally.
Thicken with Cornstarch
Mix water and cornstarch in a bowl until dissolved to create a slurry. Return the soup to a boil, add the cornstarch slurry, and stir for 3 minutes to thicken. The cornstarch gives the soup additional body and a silky consistency.
Add Cheese and Serve
Remove from heat and stir in shredded provolone until melted. Garnish with chopped parsley and extra cheese, if desired. The residual heat will melt the cheese perfectly without making it stringy or tough.