Melt butter in a saucepan over medium heat.

Add the onion, celery and carrots and sprinkle with the flour.

Cook and stir for 3 to 4 minutes and add the chicken broth.

Bring to a boil stirring constantly. Once it has started to boil, turn the heat to low and and simmer for 45 until thickened.

Puree the mixture until smooth. (If using a blender, let the mixture cool before blending. After blending, return to the pot.)

With the pot on very low heat, add half and half, cheese, and the dry mustard.

Heat until the cheese is melted and season with salt and pepper and tabasco if you choose.

Garnish with croutons.