the food that is made with wheat flour .这儿为什么用with

that is made with wheat flour .是定语从句,that指代the food.还原成独立的句子就是The food is made with wheat flour.菜是用小麦粉做的.with 用什么东西、工具from表示原料（制成品中已经看不出是这种原料了）of...