For the cake:

1. In a large bowl, whisk together oil, butter, and sugars (this should be like thick, wet sand). Stir in pumpkin puree, sour cream, and vanilla. Add eggs, one at a time, until well incorporated.
2. In a medium bowl, sift cinnamon, nutmeg, ginger, cardamom, salt, flour, and baking soda. Add dry ingredients to wet/pumpkin mixture and stir until well combined.
3. Prepare a standard cookie sheet (13″x18″) with nonstick spray. Cover with parchment paper (VERY important if making into a layer cake).
4. Pour batter into cookie sheet and spread to make a smooth, even surface.
5. Bake at 350 degrees 20-25 minutes, or until a toothpick inserted in the center comes out clean. Allow to cool completely before cutting or frosting.

To convert into a layer cake:

1. Cut a 1 1/2″ strip off of the entire border of the cake and remove (this will eliminate the rounded edges). Cut the remaining cake into three equal-sized pieces. Stack cake layers and frost as desired. Snack on any remaining edge pieces.

For frosting:

1. While cream cheese is still in it’s package, use your hands to soften it until it is just pliable (you want it to stay cold). Unwrap and place in a large bowl with brown sugar and vanilla (you can also use a stand mixer). Use a hand mixer and beat cream cheese, brown sugar, and vanilla on medium speed until mixture has lightened in color somewhat and the sugar has dissolved. (When you rub a small amount between your fingers, you should not feel any sugar grains).
2. When brown sugar/cream cheese mixture is smooth, add in about 1/2c cream and mix on medium speed until well incorporated. Add in a little more cream and repeat until all cream is incorporated. The texture should be light and feel like thick whipped cream.
3. Use to frost pumpkin bars or layer cake.