Yes, you can have dessert on a detox! Although we only have dessert on Sabbaths and feast days, not as a part of regular life. In a normal detox you will have a least one Sabbath and maybe two.
I have had some successes with replacing sugar with stevia in custard- or fruit- based desserts; replacing the sugar does not work for flour- based desserts (cake or cookies), since the sugar does more for a baked good than just sweeten it. However, flour is a no no on the detox, so we are all good!
Need to do more testing to adapt to sugar free: