Preheat the broiler.
Heat the bacon fat in a heavy-bottomed pot and saute the shallots without coloring. Add the bacon and clam juice and cook until reduced by half. Stir in 4 cups of the cream and continue cooking until again reduced by half.
Stir in the remaining 2 cups cream, the leeks, potatoes, chives and clams and season with salt and pepper. Bring the chowder to a boil, and then ladle into 4 gratin dishes. Place the chowder under the broiler until golden brown and serve immediately.
This recipe was provided by a chef, restaurant or culinary professional and may have been scaled down from a bulk recipe. The Food Network Kitchens chefs have not tested this recipe, in the proportions indicated, and therefore, we cannot make any representation as to the results.