verb/a.vwaʁ lə ky dɑ̃ l(ə) bœʁ/
to have it easy, to be rolling in money, to be rolling in it (to be extremely well-off financially thanks to one's birth in a rich family)
Probably derived from a calque of Dutch met zijn gat in de boter vallen. Literally, “to have the butt in the butter”. Compare also English land with one's bum in the butter.