Heat the oven to 225°C (435°F). Place the halved cherry tomatoes in a roasting dish with a drizzle of olive oil. Roast for 30–40 minutes until softened and lightly charred at the edges.
Meanwhile, cook the pasta in salted water according to its package instructions. Reserve a large mug of the cooking water before draining.
Let the tomatoes cool slightly, then blend with the ricotta, Parmesan, garlic and tomato paste. Add a splash of reserved pasta water and blend until smooth, adding more water a little at a time as needed. Follow your blender’s instructions for warm ingredients.
Pour the sauce into a wide pan over low heat. Season with salt and pepper, add the drained pasta and toss until coated. Loosen with more pasta water if needed.
Finish with chili flakes and serve warm.