뚝배기보다 장맛이 좋다
The taste of (soybean or red pepper) paste is better than the earthen bowl it comes in
Used to describe something that is better on the inside than it looks on the outside.
A 뚝배기 is an "earthenware bowl" Koreans use to store their soybean paste (뙨장) and red pepper paste (고추장), two staples of the Korean diet.
겉모양에 비하여 내용이 훌륭하다.
Appearances can be deceiving. Don't judge a book by it's cover.