Adjust an oven rack to the lower middle position and heat the oven to 325 degrees.
For the crust: Grind 1 box of Cinnamon Cookie Brittle to crumbs in a food processor. Blend crumbs with 2 tablespoons of melted butter. Press the cookie crumbs into the bottom of a 9" springform pan.Wrap the outside of the pan with two 18-inch square pieces of heavy-duty foil; set the springform pan in a roasting pan.
For the filling: Bring 4 quarts water to a simmer in a stockpot. Whisk the sugar, spices, and salt in a small bowl; set aside. Line a baking sheet with a triple layer of paper towels. Spread the pumpkin on the towels and cover with a second triple layer of towels. Press firmly until the towels are saturated. Peel back the top layer of towels and discard. Grap the bottom towels and fold the pumkin in half; peel back the towels. Repeat and flip the pumpkin onto the baking sheet; discard the towels.
Beat the cream cheese in the bowl of a standing mixer set at medium speed to break up and soften slightly. Scrape the beater and the bottom and sides of the bowl well with a rubber spatula. Add about 1/3 of the sugar mixture and beat at medium-low speed until combined, about 1 minute. scrape the bowl and add the remaining sugar in two additions, scraping the bowl after each addition. Add the pumpkin, vanilla, and lemon juice and beat at medium speed until combined, about 45 seconds; scrape the bowl. Add 3 of the eggs and beat at medium-low speed until incorporated, about 1 minute; scrape the bowl. Add the remaining 2 eggs and beat at medium-low speed until incorporated, about 45 seconds; scrape the bowl. Add the heavy cream and beat at low speed until combined, about 45 seconds. Using a rubber spatula, scrape the bottom and sides of the bowl and give a final stir by hand.
Pour the filling into the springform pan and smooth the surface; set the roasting pan in the oven and pour enough boiling water to come about half way up the sides of the springform pan. Bake until the center of the cake is slightly wobbly when the pan is shaken and the center of the cake reads 150 degrees on an instant-read thermometer, about 1 1/2 hours. Set the roasting pan on a wire rack and cool until the water is just warm, about 45 minutes. Remove the springform pan from the water bath, discard the foil, and set on a wire rack; run a paring knife around the inside edge of the pan to loosen the sides of the cake and cool until barely warm, about 3 hours. Wrap with plastic wrap and refigerate until chilled.
For the topping: Cover the top with whipped cream and pipe a chocolate spider web!