I have never seen a Muslim food offering at an altar. Can someone explain how it is done in the Sunni branch?
There are no food offerings, nor altars in Islam.
The closest thing are perhaps sacrifices. These are ritual slaughtering of animals, whose meat can then be eaten by the person himself and distributed among relatives, friends, neighbors and the poor. Certain sacrifices require that the meat to only be distributed among the poor. Ritual sacrifices in Islam include udhiyyah, aqeeqah, hadiy etc.
Another somewhat related practice could be where food is given as charity to the poor. This may be either as supererogatory act, or as part of an obligation like zakat al-fitr or kaffarah etc.
In any case there is no ritual in Islam where food is offered to Allah on an altar. The Quran rather negates such an act:
لن ينال الله لحومها ولا دماؤها ولكن يناله التقوى منكم
Their meat will not reach Allah, nor will their blood, but what reaches Him is piety from you.