Preheat the oven to 350º F and spray a 9 by 13-inch nonstick baking pan with cooking spray.
In a bowl, sift together flour, baking powder, baking soda, salt, pumpkin spice, and cinnamon. Whisk until combined.
In another bowl, whisk together eggs, brown sugar, vegetable oil, buttermilk, pumpkin puree, and vanilla paste until smooth.
Combine wet and dry ingredients, mixing thoroughly. Pour the batter into the prepared pan and bake for 20-25 minutes or until a toothpick comes out clean.
Once the cake is cool, make the Spiced Cream Cheese Frosting by whipping together cream cheese, butter, pumpkin spice, vanilla, and salt. Mix in powdered sugar until smooth.
Pipe rows of cream cheese frosting across the cake, then freeze for 1 hour.
For the Pourable Fudge Frosting, whisk together buttermilk, vanilla, and powdered sugar. In a saucepan, combine sugar, corn syrup, cocoa powder, and half of the butter. Heat to 240º F.
Whisk the hot mixture into the buttermilk mixture, then add the remaining butter one tablespoon at a time. Pour the mixture over the frozen cake, ensuring it covers the cake.
Tilt the pan to spread the frosting and return the cake to the freezer for about an hour or until the frosting sets.
