Step 1

Adjust oven rack 6 inches from broiler element and heat broiler. Heat 12-inch cast-iron skillet over medium heat for 5 minutes. Toss tomatoes with oil and 1 teaspoon salt. Add tomatoes to skillet and cook, stirring occasionally, until lightly charred and blistered, about 10 minutes. Stir in garlic, tomato paste, and pepper flakes and cook until fragrant, about 30 seconds. Off heat, coarsely mash tomatoes using potato masher.

Step 2

Stir in pasta and water and bring to boil over medium-high heat. Reduce heat to vigorous simmer, cover, and cook, stirring often, until pasta is tender, 15 to 18 minutes.

Step 3

Stir in Parmesan and adjust sauce consistency with extra hot water as needed. Stir in basil and season with salt and pepper to taste. Sprinkle with mozzarella. Transfer skillet to oven and broil until cheese is melted and spotty brown, about 5 minutes. Serve.