In a large bowl, beat the butter, sugar and molasses together until smooth and fluffy. Add the eggs one at a time, and mix until well combined.
Sift the flour, ginger, cinnamon, baking soda and baking power into the butter mixture. Beat until well combined.
Split the dough in half and shape each half into a disc. Wrap each disc in plastic wrap and chill in the refrigerator for 60 minutes.
Preheat the oven to 350 degrees F. Sprinkle your counter or work surface lightly with flour. Use a rolling pin to roll out the first disc of dough to be 5 mm thick. Use a cookie cutter dusted in flour to cut out your cookies and then place them on a parchment-lined baking tray. Leave at least 3 cm between each cookie to let them slightly expand as they bake.
Bake the cookies for 15 minutes, or until the bottoms have become browned. Remove the cookies from the oven and let them cool for 2-3 minutes on the baking tray before transferring to a wire rack to cool.
You can roll out the leftover dough 2-3 more times to get more cookies.
To decorate the cookies, whisk the icing sugar and water in a small bowl until completely smooth. The icing should be stiff, but will spread out a little bit. To test the icing, place a small amount of icing on a piece of parchment paper and see if it spreads. Add more icing sugar if it spreads out too much for your liking, or add more water if it is too stiff.
To assemble, scoop the icing into a piping bag that is fitted with a small round tip and decorate your cookies as desired. Allow the cookies to dry for at least an hour before you pack them away.
Store these in a air-tight tin for up to a week or freeze for up to two months. Enjoy!