Preheat the oven to 180 degrees Celsius (350 Fahrenheit).
Cut the butter into cubes, and add it to a pan set over a medium heat.
Leave the butter to melt, then remove it from the heat and allow it to cool slightly.
In a mixing bowl, add the granulated and dark brown sugar together with the butter, and use a hand mixer to beat them well.
Add the egg and egg yolk, and beat again.
Sift in the flour, bicarb of soda, add the spices, and use a spatula to mix them.
Add the crystallized ginger, and mix again.
Set the mixture aside for at least 5 minutes to harden.
Line 3 or 4 baking trays with non-stick paper.
Use your hands to shape balls out of the batter the size of a walnut, and transfer them onto the baking trays, making sure there is enough room between them to allow them to spread.
Bake each tray for 11-12 minutes or until the cookies are slightly light brown around the edges.
Remove them from the oven, and leave them to cool on the tray for 30 minutes before transferring them onto a cooling rack to cool down completely.