1. Take a fondue pot and add some crushed garlic, beer and cheese into it.
2. Stir the mixture by placing it on low heat until the cheese melts.
3. Add the butter and stir it in.
4. Take a bowl and blend together the cornstarch, some extra beer and mustard smoothly.
5. Add to the fondue and stir properly.
6. Keep stirring until the mixture turns creamy and thick.