Preheat the oven to 400F. Bake the sweet potatoes whole for 1 hour with skin on, piercing them a few times first.
Once cooked and cooled, remove the skin from the baked potato and place in a bowl. Mash the sweet potato well in the mixing bowl.
Add the sweet potato, milk, applesauce, maple syrup, oil, and vanilla to a large bowl. Stir in the chia seeds and allow the mixture to sit for a few minutes.
Meanwhile, combine all of the dry ingredients together in a separate bowl.
Stir dry ingredients into wet ingredients and mix until just combined. Do not overmix.
Take a muffin tray and line with silicone muffin liners or spray each muffin round with cooking spray. Distribute the muffin mixture evenly into 18 muffin rounds, filling almost to the top. Top with a light sprinkle of chopped walnuts, if desired. Bake at 325 F for 35 minutes. Remove muffins from the oven and brush the top of each with a bit of maple syrup.
Bake another 5-10 minutes or until a toothpick inserted into the center of the muffins comes out clean with a few crumbs attached.
Allow the muffins to cool in the muffin tin before removing. Enjoy!