Preheat the oven to 450 degrees.
Steam the cauliflower in a steam basket until very tender.
While the cauliflower is steaming cook the pasta in a large pot with salted water 1 minute less than the box instructions. It will be just slightly al dente and will continue to cook in the oven. Drain and set aside.
Using a blender or food processor, mix the cauliflower and milk until it's a smooth puree. Make sure there are no clumps.
Put the cauliflower puree back in your large pot. Heat to medium low heat. Start adding the cheese one handful at a time and stir until it melts. Also add the garlic powder, mustard powder, nutmeg, salt and pepper.
Once the cheese is all melted, add the macaroni back into the pot. Stir until well combined. Taste and adjust seasonings / salt/pepper to taste. Pour the entire mixture into a casserole dish.
In a small bowl mix the panko, parmesan and olive oil together. Evenly spread the bread crumb mixture on top of the casserole.
Bake in oven 15-20 minutes or until golden brown.