Heat the oven to 350°F (175°C). Line a 9x13-inch baking pan with parchment paper, leaving overhang on the two long sides for easy lifting.
Make the crust: pulse the flour, granulated sugar, and salt in a food processor, then add the cold butter cubes and pulse until the mixture looks like coarse crumbs. (Or cut the butter in with a pastry cutter.) Press the crumbs firmly and evenly into the bottom of the prepared pan.
Bake the crust for 15 minutes, until the edges are just starting to turn golden. Set aside while you make the filling — leave the oven on.
Make the filling: whisk the pumpkin puree, granulated sugar, brown sugar, and eggs in a large bowl until smooth. Whisk in the evaporated milk, vanilla, cinnamon, ginger, nutmeg, cloves, salt, and flour until completely combined and silky.
Pour the filling over the warm crust and smooth the top with a spatula.
Bake for 40 to 45 minutes, until the edges are set and the center still has a slight jiggle when you gently shake the pan. A knife inserted near the center should come out mostly clean.
Cool in the pan on a wire rack for 1 hour, then cover and refrigerate for at least 2 hours, or overnight, until fully firm.
Lift the bars out of the pan using the parchment overhang. Slice into 24 squares with a long, sharp knife, wiping the blade clean between cuts for neat edges.
Serve chilled or at cool room temperature with a dollop of whipped cream and a dusting of cinnamon.