More important than bank account
I have a reddit account, the bank one is the sad account.
Cooking a reddit account is the act of making a fake account on reddit long before it's needed, by intermittently posting and commenting to lend credibility to the account when it's eventually put to use. Accounts can be created with the final purpose in mind already, or old or purchased accounts can be repurposed to become sock puppets.
Reasons someone might cook an account in advance include the ability to influence discussions, express controversial opinions without being immediately dismissed as a biased party (like paid or volunteer supporters who promote specific agendas, such as Israeli hasbara trolls that are paid or volunteer to astroturf support on social media to make it appear that their position is more popular than it really is), or share fabricated content that might be met with greater scrutiny if posted from a newly created account (such as individuals who cook accounts to share fake UFO videos they've made, disguising them as authentic recordings by ordinary people).
The difference between cooking an account and the expression "sockpuppet account" lies in the fact that cooking specifically involves the pre-planning of false engagement on an account over a period of time, whereas a sockpuppet account applies to any account being used for deceptive purposes.
The term "cooking" is derived from the act of preparing food over a period of time before it is ready.
"I posted that UFO video we made on the subreddit but everyone knew it was fake right away because the account was too new. So this time, I decided to try cooking reddit accounts, and spent the two months adding random comments and posts every few days. Hopefully when I post this new video they will be a lot less skeptical!"