custard (n.)

mid-14c., "meat or fruit pie," crustade, from Middle French croustade (Modern French coutarde), from Old Provençal croustado "fruit tart," literally "something covered with crust," from crosta "crust," from Latin crusta "rind, crust, shell, bark" (from PIE root *kreus- "to begin to freeze, form a crust"). Modern meaning is c. 1600. Spelling change perhaps by influence of mustard.