Dua for blessing in food
اللّهُـمَّ بارِكْ لَنا فيهِ وَأَطْـعِمْنا خَـيْراً...
اللّهُـمَّ بارِكْ لَنا فيهِ وَأَطْـعِمْنا خَـيْراً مِنْـه
Allahumma barik lana feehi wa-atAAimna khayran minh
Translation
O Allah, bless it for us and feed us better than it.
When to recite
Said by one whom Allah has provided food.
Source / Reference
At-Tirmithi 4/288