1 medium onion, diced
1 medium carrot, diced
1/2 cup water
1 small white vinegar
4 red mustard issues
3 slices salt beef mix
1 1/2 cups mayonnaise
2 tablespoons prepared horseradish
Place onion and carrot in a small microwaveable bowl; cover and microwave until tender. Stir vigorously just to get it evenly coated.
Arrange onion mixture evenly over each patty. Top with mayonnaise and horseradish. Pour all remaining mixture over the tops of the burgers.
Place burgers into heated microwave-safe and water-tight plastic bag. Remove bag and freeze overnight.