"Still not sure what expense account to post the transaction against."
Not every withdrawal of cash is an "expense" and not every deposit of cash is an "income." You took some cash out of your bank account, held the cash for a while, then re-deposited the cash. No expense, no income.
If (maybe) you're using an accounting program like Quicken and want to record the two transactions you'd enter them along the following lines:
Debit (increase) "Cash in Hand" $XXX
Credit (decrease) "Cash in Bank" $XXX
Withdrawal in the form of Cashier's check
and
Debit (increase) "Cash in Bank" $XXX
Credit (decrease) "Cash in Hand" $XXX
Redeposit of Cashier's check
