Je voudrais commander un plat du jour avec une sauce à part.

Pronunciation: zhuh voo-dreh kom-ahn-day uh plah doo zhoor ah-vek oon soss ah par

Meaning: I would like to order the daily special with sauce on the side.

This polite request is commonly used in French restaurants when ordering; "le plat du jour" is a traditional offering that changes daily and is often a good value, while asking for sauce separately shows dining finesse.