Preheat your oven to 425°F (220°C). Line a baking sheet with parchment paper or lightly grease it with olive oil to prevent sticking.

Remove the leaves from the cauliflower head and trim the stem so that it sits flat on the cutting board. Slice the cauliflower into thick "steaks" about 1-inch (2.5 cm) thick. You should get 2 to 3 steaks from one large cauliflower, depending on its size. Reserve any loose florets for another use.

In a small bowl, mix together the olive oil, minced garlic, chopped shallots, and rosemary. Brush both sides of each cauliflower steak with the olive oil mixture, ensuring they are evenly coated. Season the steaks with salt and pepper to taste.

Place the cauliflower steaks on the prepared baking sheet in a single layer, making sure they have some space between them. Bake in the preheated oven for 15-20 minutes, or until the cauliflower is tender and the edges are golden brown.

Once the cauliflower steaks are tender, remove them from the oven. Sprinkle each steak with a layer of grated Parmesan cheese, followed by a layer of shredded mozzarella cheese.

Return the baking sheet to the oven and bake for an additional 5-7 minutes, or until the cheese is melted and bubbly, and the cauliflower is caramelized around the edges.

Carefully transfer the cauliflower steaks to a serving platter or individual plates. Garnish with freshly chopped parsley for a pop of color and added freshness. Serve hot as a delicious and nutritious main course or as a side dish alongside your favorite protein.