1 1/2 teaspoons baking soda
2 teaspoons ground ginger
1 teaspoon ground cinnamon
1/4 teaspoon salt
1 stick plus 2 tablespoons unsalted butter, softened
3/4 cup sugar
1 large egg, at room temperature
1/4 cup unsulfured molasses
Filling
6 tablespoons unsalted butter, softened
2 cups confectioners’ sugar
1 1/2 tablespoons fresh lemon juice
FOUR (filling): In the bowl of a standing electric mixer fitted with the paddle, beat the butter with the confectioners’ sugar at medium speed until light and fluffy, about 3 minutes. Beat in the lemon juice (I doubled the amount of lemon required for a more tart taste – worked out great).
FIVE: Arrange the cookies in pairs on a large work surface. Spoon or pipe 1 rounded tablespoon of the lemon filling onto the flat side of half of the cookies. Sandwich with the remaining cookies, pressing them together so the filling spreads to the edge.
Make Ahead: The sandwich cookies can be stored in an airtight container between sheets of wax paper for up to 1 week.