How to Make It
In a large pot of salted boiling water, cook the pasta until al dente, about 8 minutes. Drain the pasta, reserving 1/2 cup of the cooking water.
Meanwhile, in a large, straight-sided skillet, heat the 1/4 cup of olive oil. Add the onions, season with salt and toss to coat with the oil. Cook over high heat until the onions are just beginning to soften, about 1 minute. Stir in 3/4 cup of water and cook until the water is evaporated and the onions are just tender, about 6 minutes. Stir in the guanciale and cook, stirring, until the fat is rendered and the guanciale is lightly browned and crisp, about 7 minutes.
Carefully drain off all but 2 tablespoons of the fat from the skillet. Stir in the pasta along with the pecorino, radicchio and the reserved pasta water. Cook over high heat, stirring constantly, until hot, about 1 minute. Season the pasta with salt and pepper and top with dollops of the ricotta. Transfer the pasta to a large serving dish, sprinkle with the walnuts and top with a drizzle of olive oil. Serve immediately.