01 - Set oven to 375°F (190°C). Lightly grease a medium casserole dish with butter or nonstick spray.
02 - If using fresh cauliflower, pulse florets in a food processor until they resemble grains of rice.
03 - In a large skillet over medium heat, melt the butter. Add diced onion and cook for about 3 minutes until translucent, then add minced garlic and sauté for 1 minute until fragrant.
04 - Add riced cauliflower to the skillet and cook for 5–6 minutes, stirring occasionally, until slightly softened and excess moisture has evaporated.
05 - Stir in chopped spinach and cook for 2 minutes until wilted.
06 - Lower the heat to minimum. Add heavy cream, cream cheese, 3/4 cup Parmesan, 1/2 cup mozzarella, salt, pepper, nutmeg, and Italian herbs. Stir well until the mixture becomes creamy and homogenous.
07 - Transfer the mixture evenly into the prepared casserole dish. Sprinkle the remaining mozzarella and Parmesan over the top.
08 - Bake for 20–25 minutes until the top is golden brown and the sauce is bubbling around the edges.
09 - Remove from oven and allow to cool for 5 minutes. Garnish with fresh parsley before serving.