This breathing exercise most likely has another name, but it was taught to me as Layer Cake Breathing so that's what we're going with! I fully support your decision to eat cake while doing a breathing practice, however this specific exercise (sadly) does not include baked goods.
First, find your seat. This can be done in any seated position. You can also do this laying down. Laying down gives you a better feeling for your three dimensionality and brings awareness to the backside of your body so it's worth trying. Then imagine your torso was divided into three sections--a lower, middle, and upper section. Next, breathe into each section individually for five to ten breaths. Do your best to contain each breath within its specific section. Notice. Is there a section that's easier for you to breathe into? Is there a section that's more challenging for you to breathe into? Once you've worked through each section slowly inhale to continuously fill the lower, middle, and upper section. Then slowly exhale to empty from the upper, middle, and then the lower section. Work through this for five to ten breath cycles.
Consider this exercise as an exploration of your breath. Through this exploration you'll quickly become aware of your limitations. Your lungs and diaphragm are huge! And although the lungs extend all the way up to your collar bones, most people find the upper section harder to access.
Just like your asana practice, patience and consistency are key. Continue to work with this breathing exercise to focus in and explore the full capacity of your breath.