Heat 2 tablespoons of extra-virgin olive oil in a skillet over medium-low heat.
Add the finely minced onion and cook, stirring occasionally, until translucent, about 4–5 minutes.
Add the canned tomatoes with their juices and gently break them up with a wooden spoon.
Season the sauce with salt and pepper and add 6 basil leaves torn or roughly chopped; cover and simmer on low for 15 minutes, stirring occasionally, until creamy but still slightly chunky.
Meanwhile, bring a large pot of lightly salted water to a boil and cook the bucatini according to package directions for al dente, or 2–3 minutes less than the package time if desired.
Drain the pasta, reserving a splash of cooking water if you like to loosen the sauce.
Remove the sauce from the heat, stir in the remaining basil leaves, adjust seasoning with salt and pepper, then fold in the cooked bucatini until evenly coated; add a little reserved pasta water if needed.
Drizzle with a little extra-virgin olive oil and serve immediately.