Let's assume that the casserole contained cereal. If we say "Она съела кастрюлю каши" it means that she ate the entire casserole and you can't say "Она поела кастрюлю каши". If you want to say that she ate some of the content you may say: "Анна поела немного каши." or "Анна взяла из кастрюли немного каши и съела её."Originally Posted by Pravit