Heat 3 tablespoons of olive oil in a large saucepan. Add the garlic and fry gently. After 1 minute, add the whole chillies, then continue to fry until the garlic is lightly brown. Remove it with the chillies and save. Add the basil to the hot oil for a few moments to add flavour, then remove and save. Finally, add the tomatoes to the flavored oil with the red pepper flakes (if using) and the salt and cook gently for 10 minutes.
Cook the penne in boiling salted water until al dente. Drain, add to the tomato sauce, and toss to coat. Top with toasted garlic, chilies and basil. Serve with olive oil drizzled on top.