Shortened from the chengyu
画饼充饥, derived from
《三国志·魏志·卢毓传》:
魏明帝 told the official
卢毓 that picking officials by reputation alone is like
画地作饼,不可啖也 ('drawing a pancake on the ground - you can't actually eat it'). The two-character
画饼 later became the standalone verb used in modern office slang.