This is an old recipe from J. L. Hudson's Department Store in Detroit, which was opened in 1911. In 1963 they closed the shop because the downtown area had become less than safe and they simply could not attract customers.
Melt the butter in a large saucepan; add onion, celery and carrot. Cook gently stirring often (about 10 minutes) until vegetables soften. In a small dish, mix flour, corn starch, paprika and baking soda together. Add to vegetables and cook stirring constantly for 1 minute. Slowly add milk and broth and whisk til smooth. Heat to a simmer; cover and cook gently stirring often (about 10 minutes) til carrots are tender. Remove from heat; add cheese SLOWLY and stir til smooth. Add Bitters, salt and pepper to taste and stir til incorporated. Serve hot with a sprinkling of parsley.