Peel and cut the sweet potatoes into 1-inch cubes. Add them to a small pot with 1/2 cup of water. Cover the pot with a fitted lid and turn the heat to medium-high. Let them steam for 15 minutes or until they are tender. Mash them into a smooth consistency and measure out 2/3 cup.
Add the apple cider vinegar and plant-based milk to a large bowl. Let it sit for a few minutes to allow time for curdling. Whisk in the sweet potatoes, melted vegan butter, and vanilla extract.
Add the flour, cane sugar, cinnamon, baking powder, baking soda, salt, and nutmeg to the large bowl. Gently fold everything together.
The consistency of the batter can vary here depending on how moist the sweet potatoes were. If it's sitting on top of the spoon in a big heap, add a little more plant milk. If the batter is running off the spoon, add more flour. We want it to be thick enough to slowly spill over the spoon.
Heat a large pan or pancake griddle to the medium-low heat setting. Add a small amount of vegan butter to the pan (optional for nonstick pans).
Pour 1/3 cup portions of batter a few inches apart from each other. Try not to squeeze too many pancakes into the pan so that you can easily flip them.
Flip the pancakes as soon as you see a few bubbles pop at the surface (3-4 minutes). Let them cook for another 1-2 minutes on the other side. Repeat this process until all of the batter has been used.