Preheat oven to 375 degrees F and line two cookie sheets with parchment paper. Grease parchment paper for easy removal.
Slice onions into very thin rounds, discarding outer skin. Aim for about 16 rounds.
Arrange 8 piles of the cheddar cheese on each cookie sheet.
Press an onion round on top of each pile then sprinkle with ranch seasoning.
Bake for 11-13 minutes, watching closely, Cook time will vary some based on onion slice thickness.
Allow crisps to cool for 5-7 minutes before removing from sheet.
Serve with marinara sauce or ranch dressing.
