Preheat the oven to 350°F and grease and line a 9x13-inch pan with parchment paper and set aside. Greasing the pan first holds the parchment paper in place for clean edges.
Dissolved 2 teaspoons baking powder in 1 tablespoon water in a prep bowl. Set aside.
In a large bowl with a hand mixer or a stand mixer fitted with a whisk attachment, mix together 2 cups granulated sugar, 1 (15oz.) can 100% pumpkin puree, 1 cup vegetable oil, 1 teaspoon vanilla extract, and the baking powder/water mixture from step #2 and beat until fully combined.
Add the 4 large eggs one at a time, mixing after each addition just until incorporated.
In a separate medium bowl, whisk together 2 cups all-purpose flour, 2½ teaspoons pumpkin pie spice, 1 teaspoon baking soda, and ½ teaspoon salt.
Add half of the dry ingredients to the wet ingredients and mix just until incorporated, then mix in the other half until fully combined.
Pour the cake batter into the prepared cake pan and bake for 30 to 35 minutes or until a toothpick comes back clean from the center.
Cool cake for about 1 hour before frosting.