Dice everything up nice, there is a lot of chopping. Saute the onion and carrot in a little butter for about 7 minutes. add in the potatoes, stock, and water and simmer until the potatoes are tender, about 20 minutes. Stir in the pickle juice, pickles, mustard, and pastrami. Bring to a simmer, simmer 5 minutes, remove from heat, and serve.