Preheat the oven to 350º. Place a rack in the lowest position.
Grease a 9x12" (1/4 sheet) pan.Cream together the butter and sugar in a stand mixer fitted with the paddle until light and fluffy. Add the molasses, then the egg, beating to combine after each. Sift together the dries, then add to the butter mixture and beat on low until just combined.Using an offset spatula or moistened fingers, press and spread the dough into the prepared pan, making it as flat and smooth as possible. (Hint: if you scrape the bowl well enough, you can reuse it for the pumpkin filling.) Place in the oven on the lowest rack, and bake for about 20 minutes, until firm. Remove and set aside. Turn the oven down to 325º.
Pumpkin Cheesecake Filling
Line a large plate with a triple layer of paper towels and spread the squash puree evenly over. Place another triple layer on top (I don't hate trees, I swear!) and top with another large plate. This will press out excess moisture and prevent a watery cheesecake. Get on with the rest of the cheesecake. When you're ready to add the squash, remove the top plate, peel off the top layer of towels, grasp the bottom layer and flip the squash onto the plate. You should have 10 or 11 oz. of puree.
Beat together the cream cheese and sugar on low in the bowl of a stand mixer fitted with the paddle attachment until very smooth and well combined, scraping down the sides of the bowl and the paddle. Add the salt, spices and squash puree and beat until combined. Add the eggs one at a time, beating until combined and scraping down the sides of the bowl and the paddle between eggs. Beat in the cream, vanilla and booze until combined, scraping the paddle and bowl to incorporate thoroughly.
Spread the puree onto the baked gingersnap crust. Place in the 325º oven on the lower rack. Bake 25-35 minutes until the sides are just barely starting to puff up a bit. The center should wiggle like jello when you jostle it, but should not seem liquidy. Remove and let cool 10 minutes.
Sour Cream Topping
Beat all together to combine. You can use a bowl and spoon for this. Gently drop spoonfuls of the mixture onto the outer edge of the cheesecake, then use an offset spatula or the back of a spoon to carefully spread the mixture to evenly coat the cheesecake. Return to the oven for 5 minutes until set. Remove.
Let the cheesecake cool to room temp, about 1 hour, then chill for at least 2. Using a sharp knife dipped into hot water and dried between each cut, slice in the pan into squares (6 the long way by 4 the short way, or whatever size you like).
Notes
Gingersnap Crust This recipe calls for half an egg. Odd, yes, so if you fancy, make a double batch of the dough and set half of it aside to roll out and cut into gingersnaps. Or just have half an egg lying around to add to a scramble or brush on a set of buns. To measure half an egg, break the egg into a bowl and beat well to combine. Measure out 2 tablespoons.I've written this recipe to be as quick and easy as possible. For an extra-delicious crust, don't spread the cookie dough directly into the pan; instead, wrap it and chill until firm, about 1 hour. Roll out to 1/8" thick, and cut into 2" squares.Place on a parchment-lined sheet pan, spaced 1" apart, and bake for about 20 minutes, until firm and slightly darkened around the edges. Let cool completely, then grind finely in a food processor. Toss the cookie crumbs with two or three tablespoons of melted butter until they clump together, then press them evenly into the pan. Bake the crust for 10 minutes until toasty, let it cool slightly, then proceed with the recipe.Pumpkin Cheesecake FillingTo ensure smooth cheesecake, have all your ingredients at room temperature. Be patient while mixing the batter, and don't skimp on scraping down the sides of the bowl and the paddle. Keep the mixer on medium-low; anything higher will incorporate too much air into the batter, resulting in unsightly bubbles in the finished product. I can think of nothing more embarrassing.Nutritional values are based on one of 24 bars.