Roast a bulb of garlic. Here is the recipe: Roasted GarlicDice an onion into ¼-½" dice.
Put 1 cup of water into the inner pot of the Ninja Foodi or the Instant Pot. Place the basket or another accessory that will hold the cauliflower into the inner pot.
Cut the cauliflower in half and remove the stem and core. The florets can be cut up or left in large pieces. Add them to the basket, put the diced onions on top and put the pressure lid on. Turn the valve to seal and set high pressure for 5 minutes. When the time is up, immediately release the pressure.
Remove the basket with the cauliflower and dump the water out of the inner pot. Put the cauliflower in the inner pot and turn on sear/sauté on high. Use a Mix 'N Masher or a wooden spoon or potato masher to break up the cauliflower and sauté it until the liquid evaporates. This takes about 5 minutes or so. Stir constantly so you don't brown the cauliflower.
When the cauliflower is pretty dry (you don't see little steam bubbles forming at the edges of the cauliflower mash), transfer it to a mixing bowl. If your inner pot is stainless steel, you can leave the mash right in the pot and proceed to the next step.
Add the bulb of roasted garlic to the cauliflower by squeezing from the bottom and the cloves will pop out. Add salt and pepper, grated parmesan cheese, butter, sour cream and mix to combine. The mixture will be chunky. Add ½ Tablespoon of heavy cream and use an immersion blender to puree the mixture if you want smooth mashed cauliflower. You can also let the mixture cool down and use a blender to puree it. If the mixture is too thick, add a little more cream. If it is too loose, add some more grated cheese or put it in a container, covered and bake it until it's the consistency you like.
Serve & Enjoy!