- 1/4 cup butter
- 1/4 cup all-purpose flour
- 1 teaspoon salt
- 4 cups milk
- 1 teaspoon mustard, or to taste
- 1 1/2 pounds Baby Swiss cheese, grated
- Melt butter in a saucepan over low heat. Whisk flour and salt into butter until mixture is smooth and bubbly, about 1 minute. Remove from heat and whisk milk into butter mixture.
- Bring mixture to a boil, whisking constantly; cook at a boil for 1 minute. Stir in mustard.
- Reduce heat to low and stir Swiss cheese into milk mixture 1/4 cup at a time until cheese is melted and fondue is smooth, 5 to 10 minutes.