Heat the oil and garlic in a large, deep sauté pan over medium heat. Keep the heat on medium so you don’t burn the garlic. A little brown is okay. After about 2 minutes, add the tomatoes, crushing them with your hands as you add them to the pan. Lower the heat to medium-low and cook, stirring occasionally, for about 10 minutes. You want the tomatoes cooked – not with raw tomato flavor, there’s a big difference.
Bring a large pot of salted water to a boil. Drop in spaghetti and cover the pot to quickly return the water to a boil. Cook the pasta until it is tender but still a little chewy when bitten, 8 to 10 minutes. Drain the pasta and reserve the pasta water.
Add the drained pasta to the pan along with ½ cup of the pasta water. Cook and toss the pasta and sauce together over medium-high heat until the sauce reduces in volume slightly, gets creamy, and coats the pasta. Keep the pasta moving until pasta and sauce become one thing in the pan. Taste it, adding salt and pepper until it tastes good to you but is slightly underseasoned. Add the basil leaves and toss again.
Dish out the pasta onto warmed plates and garnish with salt and pepper.