Peel the sweet potatoes and cut into thin slices. Soak in water (I soaked for about 5 minutes) and drain. Microwave for about 5 minutes.
While still hot, mash the sweet potatoes. Add the butter, honey, and lemon juice and mix well. While keeping an eye on the thickness, add the milk. You want the mixture to be thick enough for you to be able to form it into balls with your hands. It should take about 1 tablespoon of milk.
Shape into any shape you like and brush the surface with egg yolk. This time, I shaped them into lemons.
Toast in a toaster oven for a few minutes until browned and you're done.
It's easy to make shapes, so I made little ducks. The eyes are black sesame seeds.