Cook the Pasta: Bring a large pot of salted water to a boil. Add the capellini pasta and cook according to package instructions (typically 2-3 minutes since it's a thin pasta). Drain the pasta and reserve about 1/2 cup of pasta water for later.

Prepare the Tomato Sauce: While the pasta is cooking, heat 2 tablespoons of olive oil in a large pan over medium heat. Add the minced garlic and cook for about 1 minute until fragrant but not browned. Add the diced tomatoes (or cherry tomatoes) to the pan. Cook for 5-7 minutes until the tomatoes break down and release their juices. Stir occasionally. Season with salt, pepper, and red pepper flakes if using. If the sauce looks too thick, add a bit of the reserved pasta water to thin it out to your liking.

Combine Pasta and Sauce: Add the drained pasta to the pan with the tomato sauce. Toss everything together, ensuring the pasta is evenly coated with the sauce. If needed, add more pasta water to achieve a silky sauce consistency.

Add Fresh Basil: Remove the pan from the heat and stir in the fresh chopped basil. Taste and adjust the seasoning with more salt and pepper if needed.

Serve: Serve the Capellini Pomodoro in bowls, topped with freshly grated Parmesan cheese if desired, and garnish with extra basil leaves.