Recipe(tried): 1886 Cafe and Bakery Cheese Soup

I have a recipe for Cheese Soup that is from Helen Corbitt's Cookbook

1886 Cafe and Bakery CHEESE SOUP
Driskill Hotel, Austin

This recipe is hotel executive chef David Bull's adaptation of Texas cooking maven Helen Corbitt's original cheese soup. He likes it a bit spicier and he uses Velveeta, which melts beautifully. If you substitute cheddar, which was called for in the original, be sure to grate it finely or it will not melt all the way.

1/4 cup butter
1/2 cup onion, minced
1/2 cup carrot, minced
1/2 cup celery, minced
1/4 cup flour
1 1/2 tablespoons cornstarch
4 cups chicken stock
4 cups milk
1/4 teaspoon baking soda
1 pound grated Velveeta or mild cheddar
1 teaspoon dried parsley
1 dash cayenne or to taste
1 dash paprika or to taste
1 teaspoon salt or to taste
1 teaspoon white pepper or to taste

Melt butter in a heavy saucepan. Over medium-high heat, saut the onions, carrots and celery until translucent and tender, about 3 to 5 minutes. Stir in flour and cornstarch. Cook about 3 to 5 more minutes. Add stock and milk gradually, blending until smooth, and reduce by 1/4. Do not allow to boil at any point. Add baking soda and cheese and stir until melted and thickened, about 10 minutes. Add parsley, cayenne, and paprika. Keep soup warm over very low heat or in a double boiler if not using immediately. Season with salt and pepper to taste. Serves 6 to 8.