1 ounce dried porcini mushrooms
6 cans hot chicken stock (divided)
3 tablespoons butter
1 cup thinly sliced leeks (white and light green parts only)
1/4 cup thinly sliced shallots
1 cup white wine
2 tablespoons Cognac or Brandy
1 1/2 pounds mushrooms (brown or white) (trimmed and roughly chopped)
1/3 cup heavy (whipping) cream
  Freshly ground black pepper (to taste)
  truffle salt or truffle oil (as garnish)
1 tablespoon fresh minced tarragon (as garnish)
1 tablespoon fresh minced tarragon (as garnish)