Begin the recipe by preheating the oven to 350 degrees F. and line a large baking sheet with parchment paper. Set aside.
In a medium mixing bowl, whisk together all dry ingredients, 2 cups all-purpose flour, 1 ¼ teaspoons baking soda, 2 teaspoons ground ginger, 1 teaspoon ground cinnamon, ¾ teaspoon salt, and ½ cup granulated sugar.
Next using a wooden spoon or rubber spatula stir in ½ cup dark molasses, ⅓ cup vegetable oil and 1 large beaten egg until the mixture is thick, stiff, and pretty difficult to stir.
Carefully stir in the ⅓ cup hot water, this will smooth out the whoopie pie batter, and make it much easier to stir. Continue to stir the mixture until combined.
Use a cookie scoop to scoop the cookies onto the prepared baking sheet lined with parchment paper. Each individual cookie should be about one ounce each. Space about ½-inch apart, they will spread a little while baking.
Place the sheet into the oven to bake for about 12 minutes. They will still be soft due to a whoopie pie is a cross between a cake and a cookie, but be careful not to overbake.
Allow the cookies to cool on the baking sheet for about 15 minutes and then remove to cool entirely on a baking rack while preparing the pie filling.
For Filling, use an electric mixer and mix together 8 ounces of cream cheese, 2 ½ cups powdered sugar, ¼ cup butter, 2 teaspoons milk, and 1 teaspoon vanilla extract until fluffy and smooth about 2 to 3 minutes.
Add the filling to the inside of one cookie before marrying it with another cookie to create a sandwich with two sizes that are similar in size. The easiest way is to pipe the filling with a pastry bag, but feel free to use a spoon for this porcess. Continue the process until you run out of cookies. Serve and enjoy!
Store any leftovers in an airtight container at room temperature for up to 4 days.