Heat 2 Tbs. of the butter in a 4-qt. or larger pressure cooker over medium heat. Add the shallot and cook, stirring often, until soft, 4 to 5 minutes. Add the saffron, if using, and cook 1 minute. Add the rice and stir until the grains are well coated with the melted butter. Add the chicken broth (or broth and wine) and lock the lid in place. Increase the heat to high until the cooker reaches high pressure. Reduce the heat as necessary to maintain the high pressure setting and cook for 6 minutes.
Remove the pot from the heat and immediately release all the pressure (either using a quick-release feature or by running the pot under cold water, keeping the steam vent tilted away from you). Unlock and remove the lid and check the consistency of the rice and the amount of liquid.
If need be, pop the pan (uncovered) back on medium-high heat and cook, stirring, until the rice is al dente and the risotto is silky and creamy, not soupy. Remove from the heat and stir in the remaining 1 Tbs. butter, the parsley, Parmigiano, and salt and pepper to taste. Serve immediately.