Translation:I always eat my meat patties with mustard.
Just explain how it's made. Usually, when the dish is called [something]-snadder, it's some form of dices beef dish with chips/fries. 'Biffsnadder' is the standard, with diced and fried beef, chips, fried vegetables(paprika and mushrooms usually) and bearnaise sauce.
'Hvitløkssnadder' would then be diced beef spiced with garlic, or maybe with garlic sauce.