Preheat your oven to 325°F.
Season the pork with salt & pepper.
On top of the stove, heat your Dutch oven over medium high heat and add the oil. When the oil is hot and about to smoke, brown the pork on all sides. (If you do try this in a crock-pot, you still want to do this step of browning the meat. Use a large fry pan.)
Once the meat is browned, remove it from the pan and pour off most of the excess fat but leave a tablespoon or two.
Add the pearl onions, leeks and carrots and cook until the vegetables brown a little and begin to soften. This should take about 5 minutes.
Carefully add the port to deglaze the pan and scrape up any browned bits of pork that may have stuck to the bottom of the pot.
Now add the stock, pitted prunes and bay leaves to the Dutch oven and bring the liquids to a boil. Immediately turn off the heat, add the pork back to the oven and spoon some of the prunes and vegetables over the top of the meat.
Place a layer of foil over the top of the Dutch oven, cover with lid, and stick it into the oven to cook for about 1½ hours. This should take it to the 165ºF before resting. Remove the pork from the pot and cover with the foil to keep warm. The original recipe calls for skimming "off any fat from the cooking juices". Most recipes I read say this but I always find it difficult to do. I prefer to stick the liquids into a plastic container and refrigerate. After an hour or so, the fats congeal at the top and I spoon them off. I guess if you are going to serve this right away, this technique won't work and you will have to do your best skimming the fat from the juices.
Remove the two bay leaves if you can find them. Taste the sauce and adjust the seasonings with salt and pepper.