Rub the inside of a pot with halved garlic. Discard garlic. Add 8 ounces of beer to the pot, bring to a simmer over medium heat.
Meanwhile, toss grated cheeses with cornstarch and dry mustard. When beer is bubbly, add cheese mixture, one handful at a time, stirring constantly in a zig-zag pattern, blend completely between additions. Stir in horseradish. Cook just until the cheese is melted and creamy. Do not let boil. If too thick, slowly add more beer to reach desired consistency.
Transfer the cheese mixture to a fondue serving pot, set over a low flame to keep warm.
Serve with a variety of dippers, such as cubed crusty French bread, whole grain or rye breads, cubed ham, broccoli and cauliflower florets, carrots, cherry tomatoes, chopped bell peppers, or peeled and chopped apples and pears. Spear your choice of dippers with a fondue fork, dip into cheese, and devour!!