Prepare the Pretzel Nuggets according to the package directions.

Melt the butter in a saucepan over medium heat. Add the flour and cook, stirring for 1 minute. Gradually whisk in the milk and cook, uncovered, until the mixture has thickened. Remove from the heat and stir in the cheese and mustard. Continue stirring until the cheese is fully melted.

Serve the hot pretzel nuggets with warm cheese sauce.