Preheat oven to 350 degrees F.
Butter a 10 inch cast iron skillet. Set aside.
In a large mixing bowl, add the butter, both sugars, pumpkin, eggs, and vanilla. Beat with an electric mixer for 1 minute.
In a separate bowl, whisk together the flour, baking powder, salt, pumpkin pie spice, and cream of tartar.
In three increments, add the flour mixture to the butter/sugar mixture. Scrape the sides of the bowl.
When all ingredients are combined, beat on medium-high speed for 1 minute.
Spoon the batter into the prepared cast iron skillet. Spread to the sides.
To make the sugar sprinkle, combine the 1/2 cup sugar and 1 teaspoon pumpkin pie spice in a small bowl. Whisk to combine. Sprinkle over batter.
Sprinkle salted caramel morsels on top of the sugar sprinkle.
Place skillet in center of oven. Bake for 40 minutes.
While the cake is baking, make the brown sugar whipped topping. Add the brown sugar and cinnamon to the 8 oz. container of whipped topping. Stir well. Refrigerate until ready to use.
Cake will rise in the middle and is done when a knife inserted in center comes out clean. The top will be firm to the touch.
Cool on wire rack for 20 minutes. Serve with brown sugar whipped topping or ice cream.