They are both about a romance between the king, and a lowly peasant who later becomes one of his concubines. There is also hate towards the main lead girl due to her low social status, and if you have seen Dong Yi, Yi San is King Sukjon's (the king in Dong Yi) which is also the king in Jang Ok Jung, is his great-grandson.
They are both cute dramas with romantic comedy. Even though Choco Bank is a short web drama, the story line is similar. Both main lead girls have something to do with baking or in Choco Bank's case making chocolate. The point is that they surround their passions around sweets. Both of the name also have a symbol or significance in their lives. Choco Bank's main lead girls name is Cho Co, which means chocolate in Korean, while Panda and Hedgehog main;s girl lead in Pan Da which she always have pandas figurines or something similar. The same case is with the males, each of their names mean Bank (Choco Bank) and Hedgehog (Panda and Hedgehog). Also the main girl need the main lead guy because he has a talent of sorts that is needed for their future or goals. And of course a love triangle, even though in Choco Bank is almost non-existent.