Preheat oven 325°F. Lightly spray Whoopie Pie Pan with nonstick cooking spray.
In large bowl, sift together the flour, baking powder, spices and salt. In second bowl, beat butter and sugars with electric mixer on medium speed until light and fluffy, about 3 minutes. Add egg and vanilla; beat until well combined. Add half the dry ingredients into the butter mixture and mix on low speed. When dry ingredients are almost incorporated, add milk. Continue to mix on low speed until all ingredients are almost incorporated. Add the remaining dry ingredients. Mix on low until just combined. Spoon 2 tablespoons batter into each cavity; spread batter to the edges. Cavity should be about 2/3 full.
Bake 11-13 minutes or until the top of the cake springs back when touched. Allow the cakes to cool in pan 8 minutes. Remove from pan and cool completely before filling. To assemble pies, spread about 1 tablespoon lemon filling on flat side of one cake; top with second cake.
Makes 12 whoopie pies (24 cakes total).