MELT butter in large Dutch oven over medium heat. Add onion and celery, and saute 5 minutes or until vegetables are tender. ADD chopped potato, milk, and broth; bring to boil, stirring occasionally. Reduce heat and simmer around 20 minutes, stirring occasionally. Once potatoes are tender, remove from heat and stir in half of the pimentos. Add Cheddar cheese and next 4 ingredients, stirring until the cheese melts. Let cool 5 minutes. PROCESS mixture until smooth, in batches. Stir remaining half of pimentos to serve.