Preheat the oven to 350-degrees F.
Line a 9×13-inch baking pan with parchment paper and spray with cooking spray.
Mix granulated sugar, brown sugar, pumpkin puree, buttermilk, eggs, oil and vanilla in a large mixing bowl with a whisk or an electric hand mixer.
Sift the flour into a bowl. Add the salt, baking soda, powder, cinnamon, nutmeg, cloves and ginger. Combine the dry ingredients into the pumpkin batter using an electric hand mixer or a whisk until completely combined.
Pour the batter into prepared baking pan.
Bake for 45-minutes, or until a toothpick when inserted into the center of the cake comes out mostly clean with a few moist crumbs.
Remove the cake from the oven and let cool on a baking rack. Let the cake cool for 45-60 minutes.
Make the frosting; in a large bowl using an electric hand mixer beat the cream cheese and vegetable shortening together on medium/high speed until smooth and creamy. Add the powdered sugar, vanilla extract, salt and evaporated milk. Beat on high speed for 2-3 minutes, adjust the powdered sugar as needed for a thicker frosting.
Spread the frosting on the cooled cake with a spatula.
Remove the cake from baking pan and cut into squares. Add decorative candy pumpkins if desired.
Serve immediately or cover the cake and refrigerate until ready to serve. Refrigerate any leftovers in an airtight container for up to 4-5 days.