Add the olive oil into a pressure cooker, season the pork with salt and pepper; brown on all sides over high heat.
Remove the pork from the heat and set aside on a plate. Add the garlic, white wine and chicken stock to the pressure cooker. Heat over high heat, and scrape the bottom of the pan to loosen the brown bits.
Put the pork back into the pressure cooker, close and cook for 45 minutes after it starts whistling.
Carefully open the pressure cooker after the steam has gone, add the onion and fennel and close the cooker again. After it starts whistling, cook for 20 more minutes.
Remove the pork and vegetables from the pressure cooker and keep warm. Put the pressure cooker, uncovered, over medium high heat and reduce the sauce for several minutes. If it is too thin, you can add a tablespoon of flour to thicken the sauce, stirring constantly.