Preheat the oven to 350°. In a small bowl, blend the ricotta with the chives and season with salt and pepper.
Spread 1 tablespoon of the butter in a 9-by-13-inch baking dish. Sprinkle the Parmesan over the bottom of the dish.
Bring a medium saucepan of salted water to a boil. Have ready a large bowl of cold water. Cut the pasta sheets into eight 6-inch squares.
Add the sheets to the boiling water and cook them until tender, about 2 minutes. Using a slotted spoon or a Chinese wire skimmer, transfer the sheets to the bowl of cold water and let cool. Spread the sheets on paper towels and pat dry.
Transfer the pasta sheets to a work surface. Spread 1/4 cup of the ricotta filling at one edge of each pasta sheet and roll up loosely to make flattened cylinders.
Transfer the cannelloni to the prepared baking dish and spread 1/2 tablespoon of the butter over them. Bake the cannelloni for about 12 minutes, or until heated through.
Meanwhile, in a medium skillet, heat the olive oil. Add the leeks, season with salt and pepper and cook over moderately low heat, stirring occasionally, until softened, about 8 minutes.
Increase the heat to moderate. Add the shrimp, season with salt and pepper and stir occasionally until the shrimp are cooked, about 3 minutes.
Add the Armagnac and carefully light it with a long-handled match. When the flames die down, swirl in the remaining 1 tablespoon of butter. Spoon the leeks and shrimp over the cannelloni and serve.