Place tomatoes in a large bowl and crush them by hand.
Heat olive oil in a medium sauce pan over medium-high heat. Add onion and sautè, stirring occasionally with a wooden spoon until softened and translucent, about 5 minutes.
Add the garlic and cook briefly until garlic is lightly browned, less than 1 minute.
Add The crushed tomatoes with their juices to the pan. Add 1/2 cup of water season with salt & pepper, and bring to a simmer. Turn heat to low and let simmer until thickened, about 20 minutes. At the very end of cooking, tear the basil leaves into pieces with your hands and stir into the sauce.
Bring a large pot of salted water to a boil and add the Tagliatelle. Cook uncovered over high heat until al dente.
Drain the pasta and toss with half of the sauce. Dish pasta out into individual serving plates and top with a little more sauce. Spoon 2 tbsp. of the fresh ricotta on top of each dish of pasta and serve.