If you’ve ever wondered why so many of the cakes of the Old World are so chock-full of spices and rich, sweet ingredients, Fat Tuesday provides a little insight. It precedes Ash Wednesday, which, in addition to its significance as a holy day of repentance, kicks off the longest period of fasting in the Catholic calendar: Lent, which lasts 40 days.
So then, the Tuesday before is obviously when a lot of folks party down, doing all the things they won’t get to do until after Easter. It’s also the day, historically, when cooks and bakers — in anticipation of the leaner diets of the Lenten season — would use up all the rich and/or perishable items in the pantry, often pitching them all into the same big cake. Use it or lose it, being the operative thought.
Since we live in an anything-at-anytime, on-demand society now, the impulse to use up what’s in the larder ‘lest it spoil isn’t around so much anymore. However the aesthetic survives in things like Mardi Gras king cakes, which still have that everything-but-the-kitchen-sink look to them.