In a 3-6 quart slow cooker, stir together the diced tomatoes, crushed tomatoes, garlic, cream, cornstarch, Italian seasoning, salt, basil, oregano, pepper, and red pepper flakes.
1 (14.5-ounce) can diced tomatoes, 1 (14.5-ounce) can crushed tomatoes, 4-6 cloves garlic, ½ cup heavy cream, 2 Tablespoons cornstarch, 2 teaspoons Italian seasoning, 1½ teaspoons kosher salt, 1 teaspoon dried basil, 1 teaspoon dried oregano, ½ teaspoon black pepper, ¼ teaspoon crushed red pepper flakes