1 1/2 cups water
1 1/2 cups milk
1 1/4 cups flour
1 tablespoon Worcestershire sauce
1 pound thinly sliced Swiss cheese
1 teaspoon dry mustard
In a large saucepan, water and milk are simmering. Stir in the flour. Bring to a simmer. Reduce heat to medium-low. Slowly pour in the 1 cup of water. Cook, stirring, until mixture is thickened.
Return butter mixture to a boil, stirring constantly, and cook, stirring constantly, for 2 minutes, or until a sauce-like consistency is reached.
Remove from heat; stir in cheese, dry mustard, and Worcestershire sauce. Continue to heat, stirring, until warmed through. Serve in sandwiches or with forks.