Cook pasta al dente (around 1 minute less than lowest recommend time on package directions e.g. if it says 6-8 minutes cook for 5 minutes). Set pasta aside in the colander. Add cauliflower florets and 1/4 cup water to a microwave safe bowl. Microwave for 5 minutes, or until fork tender.
Preheat oven to 400 degrees F. To a high powered blender, add hot cauliflower (plus any liquid left in the bowl), garlic, dijon, butter, mascarpone, sea salt, garlic powder, onion powder and black pepper. Puree until smooth (you see a bit of graininess but you don’t want any chunks). I suggest holding a towel over the top to prevent splattering.
Add cauliflower sauce to a large pot, along with 1 1/2 cups grated cheddar cheese. Turn heat to medium-low and stir until cheddar is completely melted. Turn off heat and add cooked pasta; toss to coat completely. Add mac and cheese mixture to a cast iron skillet or similar-sized baking dish and sprinkle with remaining 1/2 cup cheddar cheese and parmesan, if using. Place in the oven and bake for 20 minutes. Enjoy immediately; just be careful of heat. Mac n Cheese will keep for up to 5 days tightly sealed in the fridge. Try not to put into your Tupperware until it is completely cooled, or leave the lid off if it isn't. You want to prevent condensation from forming. NOTE: the leftovers will have a sulfuric smell because of the cauliflower; but you won't taste it!