Preheat oven to 400°F (200°C). On a large baking sheet, arrange tomatoes and bell pepper cut-side up. Add unpeeled garlic cloves. Drizzle with olive oil and balsamic vinegar, sprinkle with oregano, salt, and pepper.
Roast for 25-30 minutes until tomatoes are caramelized and garlic is soft. Let cool slightly, then peel garlic.
Meanwhile, in a Dutch oven, melt butter over medium heat. Add onion and carrots, cooking until softened and onion is translucent (8-10 minutes).
Stir in tomato paste and cook until it darkens slightly, about 2 minutes.
Add roasted vegetables, canned tomatoes, and broth. Drop in the Parmesan rind if using. Bring to a gentle simmer and cook for 15 minutes.
Remove Parmesan rind. Using an immersion blender (or transfer to a standard blender), puree until smooth.
Return to heat and add pastina. Cook for 6-8 minutes until pasta is tender.
Stir in heavy cream and fresh basil. Season with salt and pepper to taste.