2 cups Italian Chestnuts roasted, shelled and skinned
2 Shallots chopped
2 Leeks chopped (white and pale green parts only)
3/4 stick Unsalted Butter
2 tablespoons Dry White Wine
1/2 Fennel coarsely chopped
1 cup Chicken Broth
2 1/2 cups Water
1/4 cup Half and Half
Coarsely chop chestnuts, reserving 1/3 cup for garnish.
Cook shallot and leeks in 2 tablespoons butter in a 5-quart heavy pot over moderate heat, stirring, until softened.
Add wine and simmer until almost all liquid is evaporated, about 1 minute.
Stir in fennel, broth, chestnuts (excluding garnish), and water, then simmer, covered, 20 minutes.
Stir in half- and-half and cool mixture slightly.
Purée mixture in batches in a blender until smooth, transferring to a bowl (use caution when blending hot liquids).
Return soup to pot and bring to a simmer, thinning with water if desired. Season with salt and pepper.
While soup is reheating, heat remaining 4 tablespoons butter in a 10-inch heavy skillet over moderately high heat until foam subsides, then sauté reserved chestnuts with salt and pepper to taste, stirring constantly, until crisp and butter is browned, about 4 minutes.