Preheat the oven to 350°F. Spray a 9x13 baking dish with baking spray, set aside.
In a medium bowl, stir together the flour, baking powder, and pumpkin spice, set aside.
In the body of a stand mixer with the paddle attachment, mix together the brown sugar and butter until combined. Add the eggs one at a time, mixing in the first one fully before adding the next one.
Mix in the mashed sweet potato and vanilla.
Add ⅓ of the flour mixture, stir to combine. Add half of the milk, and mix it in. Repeat with ⅓ of the flour and the remaining milk. Add the last ⅓ of the flour, mix it in, then mix in the bourbon, scraping down the sides as needed.
Smooth the batter into the prepared baking dish and bake for 35-40 minutes until a toothpick inserted into the center comes out clean. Let cool completely.
While the cake cools, make the frosting. In the body of a stand mixer with the paddle attachment, add the butter and mix with the powdered sugar a little at a time until fully mixed in.
Add the heavy cream and maple extract, stir to combine. Turn the speed up to medium-high and whip for 3 minutes until light and fluffy.
Once the cake is cool, add the frosting. Cut and serve with caramel sauce.
Notes
You can make this non-alcoholic, replace the bourbon with milk.
The caramel sauce is amazing on this, but completely optional.
Other frostings can be used, cream cheese, regular vanilla buttercream, a cinnamon buttercream, etc.
You can add additions to the cake batter, see above for some suggestions.