Preheat your oven to 350°F (175°C) and grease a jelly roll pan (10x15 inches) with butter or cooking spray. In a large mixing bowl, beat together 4 large eggs and 2 cups of granulated sugar until fully combined and slightly frothy. Stir in ¾ cup of melted unsalted butter and 15 oz of canned pumpkin purée, mixing until the batter is smooth and well-incorporated.

In a separate bowl, whisk together 2 cups of all-purpose flour, 2 teaspoons of baking powder, 1 teaspoon of baking soda, ¾ teaspoon of salt, and 2 teaspoons of pumpkin pie spice. Ensure that the dry ingredients are evenly combined to prevent any clumps.

Gradually add the dry ingredients to the wet pumpkin mixture, stirring gently until just combined. The batter should be thick and slightly lumpy.

Pour the prepared batter into your greased jelly roll pan, spreading it evenly. Place it in the preheated oven and bake for 30 minutes, or until a toothpick inserted into the center comes out clean.

Once baked, remove the pumpkin bars from the oven and allow them to cool in the pan for at least 30 minutes.

While the bars cool, prepare the frosting by beating 8 oz of softened cream cheese and ½ cup of softened unsalted butter until smooth. Gradually add in 3 cups of powdered sugar and 1 teaspoon of vanilla extract, mixing until creamy.

Once the pumpkin bars are completely cooled, spread the cream cheese frosting generously over the surface. Refrigerate the frosted bars for about 1 hour before cutting them into squares.