Are you planning to build a business around selling it?
Do you think your friends might take your recipe and start the business you can't or won't, and then you will be envious of them?
Do you think your friends will start going to each others' homes because they will make the cake more frequently than you, and eventually they will stop coming over to your place?
Are you holding out for a "famous" recipe from one of your friends that you can trade for?
-PJ
All of the above.