Aisha Siddiqa (Radi Allahu anha) narrates that the Prophet of Allah Salam - Etiquette of Eating said,
"Whenever one eats then he should say the name of Allah (say Bis - Etiquette of Eating) and if he forgets to say Bismillah in the beginning then he should say, "Bis2 - Etiquette of Eating"
(Tirmizi, Abu Dawood, and Hakim)