Bring a medium pot of salted water to a boil. Cook the pasta according to package directions. Drain (without rinsing).
While the pasta cooks, add olive oil to a large skillet. The oil should cover the bottom by about 1/8". Heat over medium until the oil shimmers.
Add the shallots and garlic, plus a big pinch of salt, to the pan. Saute for 1 minute - the garlic should be very fragrant - and add the tomatoes and another sprinkling of salt. Reduce heat to medium-low. Stir gently to coat the tomatoes with the oil. Cover, and cook for 8 to 10 minutes. The tomatoes should be plump with their skins just beginning to wrinkle. Juices from the tomatoes will have mixed with the olive oil, and the sauce should be sturdy and flavorful.
Remove the pan from the heat. Add the basil and butter (if using), stirring gently to distribute the melting butter, but taking care not to squoosh the tomatoes. Season with another big pinch of salt and some black pepper. Taste, and add salt or pepper as necessary.
Serve family style by spreading out the pasta on a platter and topping it with the tomatoes and olive oil sauce.