Preheat oven to 350 F.
Toss cauliflower florets (24 ounces) in olive oil (2 tablespoons), salt, and pepper. Bake in a 9x13 casserole dish in the preheated oven for 25 minutes.
Meanwhile, in a large, heavy-bottom pan over medium-high heat, add olive oil (1 tablespoon). Once simmering, add the Italian sausage (1 pound). Crumble the meat into small pieces with the back of your spoon, as it cooks.
Once cooked through (no longer pink), transfer to a paper towel-lined plate. Discard all but 2 tablespoons of grease in the pan (if there isn't that much grease left, make up the difference in olive oil).
Add the chopped onion (3/4 cup), minced garlic (2 cloves), and Italian seasoning. Saute until the onion is soft -- about 5-7 minutes.
Return sausage to the pan, along with spaghetti sauce (3 cups), and heavy cream (1/4 cup).
Bring sauce to a simmer, and cook on low as the sauce thickens slightly.
Once cauliflower has finished cooking, toss the cauliflower in the red meat sauce.
In a medium bowl, combine ricotta (8 ounces), lightly beaten egg (1 large in size), nutmeg (1/8 teaspoon), and the remaining teaspoon of Italian seasoning.
Layer the ingredients in your 9x13 casserole dish, starting with half the cauliflower and red meat sauce, followed by 1/2 the ricotta mixture, then 1/2 the mozzarella and 1/2 the parmesan. Repeat, ending with parmesan on top.
Bake in the oven for 30 minutes, or until the cheese is golden. Allow it to cool slightly before slicing, and enjoy!