Buffalo Chicken Soup

Name: Buffalo Chicken Soup
Ingredients: 2 tablespoons unsalted butter; 1 tablespoon olive oil; 1 medium onion (finely diced); 2 large celery ribs (including leafy green tops, finely diced); 2 medium carrots (scrubbed and shredded); 2 large garlic cloves (minced); 1 bay leaf; ⅓ cup all-purpose flour; 2 cups low-sodium chicken stock; 2 cups milk; 2 teaspoons Worcestershire sauce; 1 teaspoon Dijon mustard; ¼-1/2 cup Frank's RedHot sauce; ½ teaspoon salt; ⅛ teaspoon black pepper; 6 ounces sharp cheddar (shredded); 2 cups cooked cubed chicken breast (or rotisserie chicken); 3 tablespoons crumbled blue cheese (for garnish); 2 scallions (white and green parts, thinly sliced (for garnish))