In a large Dutch oven, add four of the sausages and a splash of olive oil and cook on medium heat until you hear a sizzle. Lower to low and cook — it should still be sizzling — until the sausages are brown all over. It will take a while. Remove the first four sausages and then brown the rest. Remove those and pour out most of the fat, leaving about one tablespoon.
Add the onions, apples/pears, and garlic, plus a pinch of salt. Crank the heat to medium-high, stir all around, and cook, allowing the juices from the fruit to help pick up the brown bits on the bottom of the pan. Keep cooking until everything starts to brown a little (it’ll take at least ten minutes).
Add the tablespoon of flour and cook for a minute, to remove the raw flour taste. Mix the cider with the apple cider vinegar and pour some of it into the pot, stirring all around until it thickens, then incorporate the rest. Add the Juniper berries, thyme, and bay leaves, bring to a boil, return the sausages to the pot (and any juices that have collected). Put the lid on, lower to a simmer, and cook for an hour.
To finish: remove the sausages from the pot, discard the thyme sprigs and bay leaves, and bring to a boil. Reduce the sauce until super thick and viscous; taste for salt. Spoon some polenta or mashed potatoes on to plates, top with two sausages per person, and ladle on the sauce. Sprinkle with chives, if using, and serve right away.