Preheat your oven to 350°F (180°C) or 160°C if you have a fan oven. Line the cookie sheets with parchment paper or silicone baking mats.
In a bowl, stir together the flour, ginger, cinnamon, cloves, nutmeg, baking soda, baking powder, and salt.
Mix the molasses and hot water together in another bowl, and allow to cool slightly.
To the cooled diluted molasses, add the granulated sugar, vegetable oil, egg, and vanilla extract. Mix well.
Add the dry ingredients to the wet mix and stir until they're just mixed.
Use a 2-tablespoon cookie scoop to portion the dough on your baking sheets. Leave about 2 inches between each scoop. Bake the whoopie pies for 9-10 minutes or until a toothpick inserted into the center comes out clean.
Once they're out of the oven, let the cookies cool for 10 minutes on the baking sheets. Then transfer them to a wire rack to cool completely before adding the filling.
To make the Filling, Use a stand mixer or handheld mixer to whip together the softened butter and cream cheese. Add the powdered sugar, heavy cream, and vanilla and keep mixing until the frosting is light and fluffy.
Spread or pipe a generous amount of the filling on the flat side of one cookie. Put another cookie on top, flat side down, to make a sandwich. Continue with the remaining whoopie pies.
Put your 12 cookie sandwiches in the fridge for at least 30 minutes so they can firm up a bit before serving.