Preheat oven to 350F and grease a standard donut pan very well, including the centers of the donut pan.
Add all donut ingredients to a medium bowl and stir until well combined.
Divide batter evenly between 10 donut cups, filling each about three-quarters full, using a scant 1/4 cup batter per donut. (Bake in two batches if you have one 6 donut donut pan.)
Bake for 18-20 minutes, or until a cake tester inserted into the center of each donut comes out clean.
Remove from oven and let donuts cool in the pan for 5 minutes. Use a paring knife to loosen the edges of the donuts as needed and transfer to a wire rack to cool completely.
Easy Icing
Stir together powdered sugar, cocoa powder, and milk in a small bowl until icing is smooth.
Dip each cooled donut into the icing and top with crushed candy canes. Let sit for a few minutes (at least) before serving so the icing sets.
Notes
You can store these donuts for 3-5 days unfrosted in an airtight container in the fridge. They are fine to store frosted for up to 2 days, though the icing and candy canes are both more pronounced when added right before serving.
If you use sunflower seed butter, it will likely be noticeable in the flavor of the donuts. For a more neutral flavor, try almond butter.
To bake as mini muffins, use a mini muffin pan and bake for the same amount of time.
Crushing the candy canes is a great step for kids to help with. Place unwrapped candy canes into a zip top storage bag and let your kids have at it with the bottom of a measuring cup or jar.