Drizzle some oil into a medium pot set over medium-high heat, and saute the onion, celery and carrot for a few minutes, or until soft. (Crumble or slice in a sausage too, if you like, and cook it through if need be.) Sprinkle with flour and stir to coat.
Add the stock, pickles, brine, potatoes and a good grind of black pepper. Bring to a simmer and cook for 15 minutes or so, or until the potatoes are tender. If you like, serve topped with sour cream and fresh dill. Serves 4.