Makes 40 1-1/2-inch sandwich cookies
Preheat oven to 350 degrees (F), place rack in the middle position. Line baking sheets with parchment paper.
In the bowl of an electric mixer, combine sugar, butter, molasses, baking soda, ginger, cinnamon, nutmeg, salt, and lemon zest. Mix on low speed for 1 minute, then increase the speed to medium and beat for 5 minutes, until butter mixture is soft and light.
Reduce speed to low and add flour and cream. Mix until a nice dough is formed.
Using a teaspoon, scoop rounded portions, dividing dough roughly into 40 equal portions. Cut each portion in half and roll between your hands until smooth. The dough balls will look tiny, but they will spread as they bake.
Arrange on parchment-lined baking sheets, leaving 1-1/2 inch spaces between each.
Bake until cookies are golden brown and firm around the edges, about 7 - 10 minutes. Cool to room temperature.
In the bowl of a stand mixer, combine powdered sugar, butter, lemon juice, lemon extract, and salt. Beat until soft and fluffy, about 5 minutes. If frosting is too soft, add additional powdered sugar, 1 tablespoon at a time, until desired consistency is reached.
Transfer filling to a pastry bag fitted with a 1/2-inch pastry tip. (If you don't have a pastry bag, you can use a gallon-sized zip-lock bag and cut one of the bottom corners off, enough to make a 1/2-inch hole.)
Since the cookies will be slightly different sizes, match them up in pairs as best as you can. Flip one of the cookies over, pipe a heaping teaspoon of filling in the center, and sandwich with the matching cookie.
Cookies can be stored in an airtight container in the refrigerator for up to a month.