Preheat your oven to 350 degrees F (180 degrees C/160 degrees C fan-forced).
Grease a 15x10x1 inch baking pan (or 9x13 baking dish) with shortening or butter. Set aside.
In a large bowl whisk together the pumpkin puree, brown sugar, granulated sugar, vanilla extract, and oil until well combined. Beat in eggs one at a time until fully incorporated.
Combine the all-purpose flour, baking soda, cinnamon, ginger, nutmeg, and salt. Gradually add the dry ingredients to the pumpkin mixture, stirring together with a spatula until the dry ingredients are just combined with the wet ingredients.
Pour the pumpkin cake batter into the greased baking pan. Bake at 350° for 25-30 minutes (or 45-50 minutes for a 9x13 baking dish) or until a toothpick inserted in the center comes out clean.
Cool the sheet cake on a wire rack.
Cream Cheese Frosting
In a medium mixing bowl, beat the room temperature cream cheese with an electric hand mixer until smooth with little to no lumps left. Add butter and vanilla extract with an electric hand mixer until fluffy and smooth.
Gradually beat in powdered sugar until smooth. Add in splashes of milk until the frosting reaches desired spreading consistency.
Frost the cake generously and serve.