"This camembert tart is disgusting."
Translation:Cette tarte au camembert est dégoûtante.
Because «au/à la/aux is the correct preposition to use in this construction, as it is in many food related descriptions. English often does not use a preposition or uses "with" - French uses «au/à la » eg. apple pie = tarte aux pommes, clams with spinach = palourdes aux épinards, vanilla ice cream = glace à la vanille.
Prepositions are tricky little dudes that rarely translate directly between languages and I am afraid it is usually a case of having to learn them.