If you received a Form 1099-MISC to report your income from your catering gig, you are considered self-employed in the eyes of the IRS and your income and expenses must be reported on Schedule C. You are running your own business to provide your catering services, even if it was only one time.
See the TurboTax articles below for more guidance:
https://ttlc.intuit.com/replies/4771022
https://ttlc.intuit.com/replies/4801198
The links shared don't work anymore. Any way to get them fixed?
@marcotte This thread is years old. Are you trying to enter self-employment income?
SELF EMPLOYMENT INCOME/“side jobs”
https://ttlc.intuit.com/questions/2926899-how-does-my-side-job-affect-my-taxes
https://ttlc.intuit.com/community/self-employed/help/what-is-the-self-employment-tax/00/25922
https://ttlc.intuit.com/questions/2902389-why-am-i-paying-self-employment-tax
https://ttlc.intuit.com/questions/1901340-where-do-i-enter-schedule-c
https://ttlc.intuit.com/questions/3398950-what-self-employed-expenses-can-i-deduct
https://ttlc.intuit.com/questions/1901110-do-i-need-to-make-estimated-tax-payments-to-the-irs
If your self-employment income was only from cash, personal checks, credit card payments, or cryptocurrency
Type Schedule C in the Search box and then select the Jump to link. This will take you to where you can enter any cash, personal checks, credit card payments, or cryptocurrency (Form 1099-K) related to your self-employment. You may first be asked some general questions about your business. After you answer them, you’ll be taken to the Let's get income for (your line of work) screen where you can enter this income as Additional Income.