Potato Cheddar Guinness Soup

Name: Potato Cheddar Guinness Soup
Ingredients: 2 tablespoons butter; 1 medium onion , chopped (about 1 1/2 cups); 1 celery rib , chopped or sliced (about 1/2 cup); 1 1/2 pounds (680 g) russet potatoes , peeled and thinly sliced; 3 cups (750 ml) chicken stock (add 1 1/2 teaspoons of salt if using unsalted stock); 1 cup (250 ml) Guinness extra stout (do not use draught); 1/2 teaspoon fresh or 1/4 teaspoon of dried thyme; 6 ounces (170 g) grated extra sharp cheddar cheese; 1 teaspoon Worcestershire sauce; 1/8 teaspoon paprika; Chopped chives for garnish