Many times you can find just the parmesan rinds at the grocery store. Just ask at the deli and cheese counter. Otherwise buy a small piece of parmesan and cut off the rind yourself. An immersion blender is pretty critical in this recipe. You can cut the hot tomatoes and onions right in the Instant Pot without making a mess in the food processor. I tried using dried oregano but it seems all wrong in this recipe. I really like the taste of fresh herbs. If you do use dried, go easy, a little at a time and taste in between additions.