Pierce one sweet potato with a fork, wrap in a paper towel and place into a microwave-safe bowl. Fill the bowl with 1/2 inch of water. Microwave for 7-9 minutes until very tender. Allow potato to sit for 5 minutes. Peel and mash.
Peel remaining potatoes and grate into a mixing bowl. Add mashed sweet potato, eggs, almond flour, salt, and chopped onions. Mix well.
Heat coconut oil in a large skillet. Test if is hot enough by sprinkling a few drops of water into the oil. If it dances, its hot! Spoon in 2-3 tablespoons of batter for each cake. Flatten down a bit and cook approximately 5 minutes per side, allowing to brown. Continue until all potatoes have been cooked.