Preheat the oven to 350 degrees F.
Add the mashed sweet potato, grated parmesan, flour, oil and salt (if using) to a large bowl. Mix with a spoon and then when small pieces of dough start to form, knead with your hands until a ball of dough is formed.
Sprinkle a bit of flour onto a sheet of parchment paper, then place the ball of dough on top.
Place another sheet of parchment paper on top of the dough. Roll the dough between the two pieces of parchment paper until it's roughly 1/8 of an inch thick (or thinner for extra crispy crackers). Add more flour as needed so that the dough doesn’t stick.
Use a pizza cutter, pastry scraper or a knife to slice the dough into rectangular or square cracker shapes (or use small cookie cutters instead). Transfer the parchment paper with the cut crackers onto a baking sheet Next, separate the crackers on the parchment paper so that there’s space between them. Prick each cracker with a fork to prevent them from rising too much when baking.
Bake the crackers for 10-20 minutes or until the edges are lightly brown. The amount of baking time required will vary depending on the thickness of the crackers, so check on the crackers at the 8-10-minute mark and add more time as needed.
Let the crackers cool completely before serving. They will continue to harden as they cool.