Place the flour, egg whites, salt and water in a mix bowl and mix together. I usually use a fork to incorporate all the ingredients. You could also use a whisk or immersion blender. You are looking for a thin batter that easily pours off of a spoon. See photos above in the body of this post.
Preheat a skillet over low-medium heat or preheat a griddle set to 300℉.
Use a ¼ c measuring cup and fill it half-way with batter or use an ⅛ c measuring cup if you have one.
Place the batter into the skillet or onto the griddle and quickly take a soup spoon and use the back of it to spread the batter out into a thin disc or circle. See photos above in the body of the post.
The shell will cook quickly drying out on the surface - as soon as it does, take a fork and flip over and let it cook on the other side for 30-60 sec.
Remove the shell from the skillet or griddle and transfer it to a clean dish towel to cool.
As soon as the manicotti shells are cooled, they can be stuffed with your favorite filling and baked.
If you are not going to use the manicotti shells immediately, stack them and place them in an air tight container and refrigerate up to 3 days until ready to use.