In a medium (3-quart) saucepan, heat the olive oil over medium-high heat. Add the pancetta and cook, stirring frequently, until brown and crispy, about 6 to 8 minutes. Remove the pancetta to paper towels to drain. Set aside. Discard any cooking juices in the pan.
In the same pan, over medium heat, add the butter. Add the onion and cook for 5 minutes until soft. Add in the rice and stir until the rice is lightly toasted and coated with the butter, about 1 minute. Stir in the stock, salt and saffron. Bring the mixture to a simmer and, with a wooden spoon. scrape up the brown bits that cling to the bottom of the pan. Cover the pan with a tight-fitting lid and cook until the rice is tender and all the liquid has been absorbed, about 20 to 25 minutes Let the rice stand for 5 minutes. Using a fork, fluff the rice and transfer to a serving bowl. Top with the cooked pancetta and serve.