In a medium mixing bowl, whisk together both sugars, cinnamon, salt, flour and graham cracker crumbs. Add cooled, melted butter and stir with a fork until coarse crumbs form. Set aside.
!to make the cake:
Preheat the oven to 350° F.
Grease and flour a 13" x 9" baking pan. Set aside.
In a large mixing bowl, whisk together the dry ingredients: flour, baking powder, baking soda, brown sugar, granulated sugar, salt and pumpkin spice.
In another bowl, whisk together pumpkin puree, eggs, vanilla, oil and buttermilk.
Add the wet ingredients to the dry ingredients and whisk together until smooth. Whisk for about a minute (I use a whisk but you can use a hand-held mixer).
Pour the batter into prepared pan. Tap the pan against your counter to release any air bubbles.
Sprinkle the crumb topping all over the surface of the cake batter, spreading it evenly.
Bake the cake for 32 to 35 minutes OR until a toothpick inserted in few places near the center comes out clean.
Cool to room temperature and slice.
Notes
You can half the recipe for an 8" x 8" baking pan.
Please note, that the nutrition value can vary depending on what product you use. The information below is an estimate.