According to the sunnah of the Prophet (PBUH) and Ahl al-Bayt w, when one is fasting is it better to:
1. Break the fast before offering Salat al-Maghrib.
2. Offer Salat al-Maghrib, break the fast and only then offer Salat al-Isha.
3. Offer Salat al-Maghrib as well as Salat al-Isha before breaking the fast.

Number 2 above is highly recommended.