This must be obvious but, the word Omelette nonetheless method Omelette. Even if you say Du or Au or something else after it. And Fromage nonetheless means cheese no matter what other phrases you place around it. Omelette Du Fromage still manner “Omelette“ .. “Cheese”. Du fromage simply way “cheese”. It's a novel form, so it extra especially way “that cheese” in place of “some cheese”.
So certainly the phrase “Omelette du fromage” IS a legitimate word, IF the character turned into talking approximately a totally specific cheese. Like a specific type they offered a previous day and had already been discussing with a person if they then cautioned they should make an omelette with that precise cheese, then you may emerge as pronouncing: omelette du fromage
however, it'd probably nevertheless sound out of the area
it'd be like announcing: “I'm going to make: Pie this Apple.” to say you are making a pie out of this specific apple, however, you're worried it would be misconstrued if you used the right word: “I'm going to make: this Apple Pie” because that precise word ought to ALSO suggest you were talking about the specific pie, no longer the apple.
In fashionable we just know as human beings that it's going to be misunderstood so we just presuppose that we must add plenty greater detail by pronouncing: “I am going to make a Pie out of that apple”
which means even the French would possibly be given the word: Omelette du fromage on certain occasions.