Rub inside of heavy pot or saucepan with cut sides of garlic, then discard the garlic. Add beer and bring to a simmer over moderate heat.

Coat the grated cheese with the cornstarch. Gradually add cheese to pot and cook, stirring constantly in a zigzag pattern to prevent cheese from balling up. Do this until cheese is just melted and creamy, but do not let boil.

Stir in the Worcestershire sauce, dry mustard and ground nutmeg. Bring fondue to a simmer and cook, stirring, until thickened, about 5-8 minutes. Do not overcook or fondue will get stringy. Transfer to a fondue pot set over a flame.