In a bowl mix flour, baking soda, ginger, cinnamon, allspice and salt. In a separate bowl, whisk together butter, sugar and egg, then slowly stir in molasses. Gradually add in the dry mixture, stirring until incorporated.
Chill the cookie dough for at least 30 minutes, or up to 2 hours, this will help the cookies maintain their shape while being baked.
Preheat fan forced oven at 160C°, and line a baking tray with baking paper.
Make rounded scoops with the batter and place on the baking tray overlaid with non-stick baking paper. Bake for 12-15 minutes. Let the cookies rest of the pan for least 10 minutes before transferring to a wire rack.
To make the filling combine butter and cream cheese in a large bowl and beat it on medium-high speed with an electric mixer until light and fluffy. Change the mixer to low speed and gently add the icing sugar, keep whipping the mixture until all the sugar has dissolved and incorporated. Add sea salt, lemon juice and lemon zest.
To assemble the sandwiches, divide the filling among half the cookies, spreading out to the edges, then lightly sprinkle with some more lemon zest. Serve with a cold glass of milk!