Preheat an oven to 180c (350f) and prepare a 10x15 cookie sheet pan (or a jelly pan) with softened butter.
Into a large mixing bowl, add the melted butter, oil, kosher salt, eggs, ginger, nutmeg, cinnamon, pumpkin puree, and vanilla extract, and mix with a whisk until well combined.
Add the granulated sugar, and the brown sugar and mix well.
Add the flour, baking powder, and baking soda, and mix until just combined and there are no streaks of flour showing.
Butter the pan with softened butter and pour the pumpkin batter into the pan and smooth it out using a spatula. Bake in a 180c (350f) preheated oven for 20-25 minutes or until a toothpick inserted into the cake comes out clean.
Let the bars cool to room temperature before frosting. This step prevents the frosting to melt off the bars.
Make the frosting
Into a large bowl add room temperature butter and mix with a hand mixer or a stand mixer until the butter is light and fluffy.
Add the cream cheese and mix until smooth. Then add ½ of the powder sugar at a time (you don’t want to be in a powder sugar cloud).
Add a pinch of salt, and the vanilla extract and mix well until smooth.
Top the cooled bars with a layer of cream cheese frosting, and smooth it out with a spatula. Sprinkle the top with cinnamon and serve!
Notes
Use room temperature ingredients. It is important that you use room-temperature ingredients like eggs and butter. This step ensures that your mixture mixes into a homogenous mixture and bakes perfectly. you don’t want to place cold batter into the oven.
Measure your flour correctly! When measuring your flour, avoid scooping it with a measuring cup. Instead, stir the flour with a spoon to create as many air pockets as possible, and spoon it into your measuring cup. Finally, level it with a back of a knife.
Don’t overmix the batter, you don’t want to develop the gluten in the flour. This step ensures you have a moist bar and not a dense and dry bar.
Be patient! I know it’s extremely tempting to eat these bars as they are pulled out of the oven, but let the bars cool for at least 20 minutes so they will be more firm and won’t crumble up. These bars are extra moist and melt-in-your-mouth delicious, so it will be worth it to wait these 20 minutes.