Preheat your oven to 325 degrees. Spray a 9×13 metal pan on the bottom, line with parchment paper, and spray again. If you need to use metal binder clips to hold down the sides, remember to use metal, not plastic. Set aside.
In a medium size bowl, whisk together the baking powder, ground ginger, nutmeg, ground cinnamon, cloves, and all-purpose flour. Set aside.
In a stand sized mixer fitted with the paddle attachment, cream the room temperature butter, dark brown sugar, and granulated sugar until light and fluffy. About 5 minutes.
With the mixer on low speed, add the molasses and vegetable oil. Mix just until combined. With a rubber spatula, scrape down the sides and bottom of the bowl.
Add the eggs, one at a time, and mix on medium speed for 20-30 seconds after each addition. Scrape with a rubber spatula after each addition.
Add the vanilla extract to the creamed mixture. Mix on low until smooth.
Scrape the bottom of the bowl and gradually add a third the dry ingredients followed by half of the buttermilk. Mix on low just until combined. Repeat this step until you end on the flour mixture.
Pour the batter into the prepared sheet cake pan and smooth the top with a spatula.
Bake in the preheated oven for about 45-50 minutes or until a toothpick inserted into the center comes out with a few moist crumbs.
Let it completely cool in the cake pan. While the cake cools, make the caramel.
For the caramel sauce.
In a medium sized sauce pan, stir together the water, sugar, and corn syrup.
On medium heat, bring the sugar to a boil. The bubbles will start off fast and small, but once it starts caramelizing, the bubbles will slow down and become a little bigger. Do not touch or stir the mixture. That will cause crystallization.
Let the mixture boil until it becomes caramelized and looks golden brown. This does take a few minutes, but once it starts turning brown, it’s easy to burn it, so keep an eye on it.
Put the cream in the microwave for 1 minute.
Once the caramel is golden brown and ready for the cream, turn off the heat on the sugar mixture and add the warm cream. Mix the caramel mixture until evenly combined.
Pour the mixture into a bowl. Add the vanilla, salt, and butter and let it sit until the butter melts. Stir, once the butter is melted.
For the cream cheese buttercream
In the bowl of an electric mixer, combine the butter and cream cheese. Beat on medium speed for about 2 minutes. Scrape down the sides and bottom of the bowl. Beat again for 2 more minutes.
With the mixer on low, add the powdered sugar, followed by the cream, vanilla extract, and a pinch of salt. Beat on low just until combined. With a rubber spatula, scrape down the sides of the bowl.
Turn the mixer up to medium-high speed and beat for about 3 to 5 minutes.
With a rubber spatula or a wooden spoon, beat out all of the air pockets by hand for a smooth look.
Assembly
You can leave the cake in the pan. Once it’s completely cool, you can frost the cake with the cream cheese frosting. Add dollops of caramel sauce to the frosted cake (you will only need about half of the caramel. Serve the other half on the side of each piece of cake). Swirl the caramel into the cream cheese buttercream. Serve at room temperature.