This is when a woman shits in a paper muffin cup and her partner cums on it. They both eat the delicious baked good together. Sometimes, if it is the right time of the month, the woman may add some of her menstrual blood to make a pinkish frosting, mixed with the man's ejaculatory juices. It is also likely that the fresh poop will be hard to eat, so it is common for the muffin to be cooled in the refrigerator so it can harden a little. No one has ever actually tried to bake this concoction before, and it is not suggested to do so, and may result in the oven having to be replaced.
It may also be known as a butt muffin, chocolate truffle, or butt cake.
Man 1: Me and Sheila did some delicious baking last night.
Man 2: Oh yeah, what'd you bake, some buttcake cup muffins?