Cook the pasta: Bring a large pot of salted water to a boil over high heat. Add the pasta and cook until al dente, 6 to 8 minutes. Drain the pasta, reserving ⅓ cup of the pasta water.

While the pasta cooks, sauté the tomatoes: Heat the olive oil in a large skillet over medium heat. Add the onion and sauté until tender, 5 to 6 minutes. Add the cherry tomatoes and garlic, reduce the heat to medium-low, and toss to combine. Cover the skillet and cook until the tomatoes are very tender and bursting, 7 to 9 minutes.

Season the tomato mixture with salt and lots of freshly ground black pepper. Add the pasta water and bring to a simmer. The mixture should form a sauce. If needed, add more pasta water.

Add the pasta and toss well to coat it in the sauce. To serve, pile portions of pasta onto plates and top each with 2 teaspoons basil and 2 tablespoons ricotta. Serve immediately.