Heat 2 tablespoons 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 to the skillet and gently crush them with a wooden spoon.
Season with salt and pepper and add 6 basil leaves, cover, and simmer on low for 15 minutes, stirring occasionally, until the sauce is 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, drain 2–3 minutes before the package time if desired.
Remove the sauce from the heat, stir in the remaining basil leaves, then add the drained bucatini to the skillet and toss to combine.
Adjust seasoning with additional salt and black pepper to taste, drizzle with a little extra-virgin olive oil if desired, and serve.