Start by sifting the flour, ground ginger, and baking soda into your large mixing bowl. Give everything a quick stir so the spice is evenly distributed. This step keeps you from biting into a clump of ginger later.
Add your cubed butter to the dry mix and use your fingertips to work it in. Keep going until the texture looks like coarse breadcrumbs, which usually takes a couple of minutes of rubbing.
Stir in the brown sugar, then make a well in the center and crack in the egg along with the molasses. Combine everything with a spoon at first, then switch to kneading by hand until you have a firm, smooth dough.
Lightly flour your work surface and split the dough in half for easier handling. Roll each half out to about 5mm thick, then press in your Halloween cutters to create pumpkins, ghosts, and gingerbread skeletons.
Transfer your cut shapes onto a lined baking sheet, spacing them a little apart. Bake for 5 to 10 minutes depending on size, watching for the edges to turn a light golden brown before pulling them out.
Let the cookies cool completely on a wire rack before icing, since warm cookies will melt your decorations. Once cooled, pipe on your icing details and let them set before serving or packaging up.