Science has now answered life's most important question: How do you cut a cake so perfectly that each slice brings a tear to the eye? (Because the cake is moist.) (Also because you made it with onions because you're an awful human being.)
It turns out that instead of cutting your cake into triangles, what you should really be doing is cutting a strip from the middle of the cake, mashing the rest of the cake together, and then quickly putting a rubber band around the whole thing in order to keep it squashed together and moist on the inside. This does sound like more hard work then just shoving the cake in the fridge with a piece of plastic wrap kind of wadded over the top, but it's supposed to ensure that your cake is just as moist on day four as it is on day one.
Of course, this method also assumes that there are people out there who are either incapable of or unwilling to eat an entire cake in one sitting. Or that there are people who don't cut tiny slices out of a cake but grab handfuls and stick them joyously into their gaping mouth holes. I don't have any experience with this — none — but if I were writing my thesis on the proper way to cut cake, that would absolutely go into the section on limitations and future directions.