Heat oven to 350ºF. Line a baking sheet with parchment paper.

In a mixing bowl, combine the first 7 ingredients (through the ginger). Mix well.

In a second bowl, beat together the butter and sugar until light and fluffy. Beat in the oil and egg; Stir in the pumpkin. Mix in half of the dry ingredients. Stir in the milk, then mix in the remaining dry ingredients.

Drop rounded teaspoons of batter onto the prepared baking sheet. Use the back of the spoon to smooth out any lumps and bumps. Bake for 12 minutes, or until puffy and cooked through. Let cool completely.

Use an electric mixer to beat together the cream cheese and butter until it's smooth. Slowly mix in the powdered sugar to form a stiff icing. Stir in the bourbon. Cover and chill until ready to use.

To assemble the whoopie pies, spoon a heaping teaspoon of filling onto the flat sides of 8 cakes. Top with remaining cakes, pressing down gently.

Store in the refrigerator, bringing to room temperature before eating.