Cook the Pasta: Fill a large pot with water, add a generous pinch of salt, and bring to a boil. Add spaghetti and cook until al dente, about 8–10 minutes. Reserve ½ cup of pasta water, then drain.

Prepare Tomato Sauce: Grate ripe plum tomatoes into a bowl. In a skillet, melt butter over medium heat. Add minced garlic and chili flakes, sauté until fragrant.

Add Tomatoes: Stir grated tomatoes and their juices into the skillet. Season with salt and pepper, allowing to simmer for 7–10 minutes until thickened.

Combine with Pasta: Add drained spaghetti to the sauce, tossing gently to coat. If the sauce is too thick, add reserved pasta water gradually.

Finish & Serve: Remove from heat, stir in chopped basil, and serve hot with Parmesan cheese and extra chili flakes.