1Melt the butter in a saucepan over medium heat; cook the onion and garlic in the butter until the onion is tender, about 5 minutes. Pour in the Worcestershire sauce and beer; bring to a boil for 3 to 5 minutes. Stir the chicken broth and mustard. Reduce heat to medium-low and pour in the half-and-half while stirring.
2Toss together the shredded Cheddar cheese and flour in a bowl; add to the liquid mixture in small batches until melted.
3Whisk together the cornstarch and warm water in a small bowl; stir into the cheese mixture; season with salt and pepper. Heat and stir until thick; serve hot.