Place butter, sugar and water in a pot and bring to a boil over medium-high heat (about 5 minutes). Continue cooking without stirring for about 8 minutes or until it starts to turn golden and reaches 300 degrees.

Remove from heat. Stir in mustard and pretzels.

Pour onto a silicone-lined baking sheet and sprinkle with salt.

Once cool, break half into small pieces and half into larger pieces.