Creamy Caprese Cauliflower Casserole Recipe

1 medium cauliflower head, washed, trimmed, cored, and cut into florets
1 cup tomato sauce
2 tablespoons tomato paste
⅓ cup heavy cream
⅓ cup grated Parmesan cheese
1 cup shredded mozzarella, divided
1 cup grape tomatoes, halved
A handful fresh basil leaves, chopped
¼ teaspoon fine grain sea salt
⅛ teaspoon ground black pepper
Pinch red pepper flakes (optional)