Preheat oven to 350 degrees F. Line cookie sheets with either parchment paper or a silicone baking mat. In a small bowl, stir together flour, baking soda, ginger, cinnamon and salt.

Beat butter and sugar at medium speed for about 2 minutes. Beat in egg and molasses. Stir in dry ingredients until just combined.

Drop doug onto baking sheets in tablespoons for larger cookies, teaspoons for smaller cookies, and place them 3 inches apart. Bake for 10 minutes for large cookies, or 7 minutes for small cookies. Let cool slightly and transfer to wire rack to cool completely.

In a medium sized bowl, mix butter and powdered sugar on high until light and fluffy. Add lemon juice and zest and beat until combined. Arrange cookies in pairs with similar sizes. Spread filling onto the flat side of one cookie and sandwich the other cookie on top. Enjoy!