Thank you, Rustler!

For anyone else interested in what this process looks like, here is a step-by-step of Rustler's instructions, as I did them (and it appears to have worked out okay).

Step 1: create the proper account.

Step 2: create a new "Bank Deposit" from the menu.

Step 3: enter the deposit information.

Step 4: create your expense, charging from the "Cash on hand for Owner's Equity" account.

Edited to so that the image says to make sure you are depositing into the correct account (rather than the "wrong account").