Put your stamps in the fridge or freezer to chill until needed. Preheat the oven to 180°C (350°F). In the bowl of an electric stand mixer fitted with the paddle attachment, on medium speed cream together the butter, sugar and molasses for 5 minutes until pale and thick. Add in the egg yolk and beat until fully combined.
Sift the dry ingredients, flour, cocoa powder, baking soda, ginger, salt (and optional spices) into the stand mixer bowl and beat on medium until the dough starts to come together.
On a lightly floured surface, turn out the dough and knead it until all the floury crumbles are incorporated. If you find it too dry, add a teaspoon of milk at a time. Flatten the dough into a disk and on a parchment paper sheet, roll out to about ¼-inch thickness. Transfer cookie dough on the paper onto a baking tray and refrigerate for 30 minutes.
Use a cookie round (slightly bigger than the stamp) and cut out the rounds. Then remove your cookie stamp from the fridge/freezer, dust with flour and press the stamp into each of the rounds ensuring that you don’t press down all the way through.
Transfer the cookies to a lined baking sheet and bake for 8 minutes. You don't want to over bake these cookies, so do a test cookie or two to figure out the best timing for your oven. The cookies will be soft when you remove them from the oven but will firm up as they cool.
While the cookies are baking, in a bowl, whisk the glaze ingredients together until they become a smooth thin glaze. Add more milk (or coffee) if the glaze is too thick; it should have the consistency of maple syrup.
Put the cookies on a cooling rack and brush them with the glaze while still slightly warm. The glaze will dry in about 15 minutes.