That is correct… homemade food sales may be done at farmers markets, but obviously that is not conducive to a custom cake business. Technically, if you found a farmers market that was open most days, you could have your buyers pick up their custom cakes from there.
Other than that, the only legal workaround would be to try to initiate an amendment to the cottage food law in the next legislative session. If you are interested in jump-starting that, I can connect you with an organization that would probably be willing to help.
The other alternative would simply be to run your business illegally. There are probably already a lot of people in your area in Nebraska doing this, and I’m not sure if the government there cares much.