Add the garlic, beer and onion powder to a large saucepan. Heat over medium heat until it starts to simmer around the edges.
Meanwhile, add the cheese and flour to a medium bowl and toss. Once the beer is simmering, add the cheese a handful at a time, stirring to melt it. Stir in the Worcestershire sauce and mustard. Cook over low heat, stirring and scraping the bottom of the pot, until all the cheese is melted, about 10 minutes.
Serve warm with sliced apples, pumpernickel or other crusty bread cubes, soft pretzels and tiny heated wieners.