Heat the oven to 350°F (175°C). Line an 8x8-inch metal pan with parchment, leaving an overhang on two sides.
Stir the graham cracker crumbs, brown sugar, cinnamon and melted butter until evenly moistened. Press firmly into the bottom of the pan with the bottom of a measuring cup. Bake 10 minutes, then lower the oven to 325°F (165°C).
Beat the cream cheese with both sugars on low speed, or with a sturdy whisk, until completely smooth, scraping the bowl well.
Add the pumpkin, flour, vanilla, spices and salt and mix until smooth. Add the eggs one at a time, mixing on low just until each disappears.
Pour the filling over the warm crust and smooth the top. Tap the pan on the counter a few times to release air bubbles.
Bake at 325°F (165°C) for 35 to 40 minutes, until the edges are set and the center still has a slight wobble.
Cool in the pan on a rack for 1 hour, then refrigerate for at least 4 hours or overnight. Lift out using the parchment and cut into 16 bars with a hot, dry knife, wiping it between cuts.