Shred both cheeses and toss them together with the corn starch until they are coated.
6 ounces mild cheddar cheese, 2 ounces Swiss cheese, 2 tablespoons corn starch
Turn on heat to fondue pot, or place a saucepan on your stovetop.
Add lager, Worcestershire, garlic, and mustard powder to the pot and heat until warm but not boiling.
½ cup lager beer, 2 teaspoons Worcestershire sauce, 2 teaspoons garlic, 1 teaspoon mustard powder
Begin to add the cornstarch-coated cheese in small amounts, stirring as you go. Wait until one batch is mostly melted before adding more. (I add about ¼ of the mixture at a time.)
Once all of the cheese is melted and smooth, you're ready to serve! If you're using a fondue set, dip your veggies, fruit, and bread into the cheese using the small fondue forks. If you made the fondue in a pot, transfer to a bowl for serving. In that case, be sure to eat it quickly before the cheese cools and solidifies.