Start by preheating your oven to 350°F (175°C). While the oven warms up, assemble all the cake and frosting ingredients in separate areas for easier access.

In a medium-sized mixing bowl, blend together the pumpkin puree, granulated sugar, vegetable oil, and large eggs. Utilize an electric mixer for a smooth, well-integrated mixture.

In a different bowl, sift together the flour, cinnamon, baking powder, baking soda, and salt. This not only combines them evenly but also aerates the mix for a lighter cake.

Slowly add the sifted dry ingredients into the wet mixture. Stir until just combined; overmixing could make the bars dense.

Pour the final batter into an ungreased 10x15-inch jelly roll pan, spreading it evenly. Bake for about 25 to 30 minutes. You'll know it's done when the cake springs back upon gentle touch.

As your cake cools, whip up the frosting. Beat the softened butter and cream cheese until creamy. Stir in the vanilla extract. Gradually add the sifted confectioners' sugar and beat until silky smooth. Once the cake has cooled, spread the frosting uniformly and slice into 24 mouth-watering squares.