2) In a large bowl, sift together the flour, bicarbonate of soda, cinnamon, cloves, nutmeg, ginger and salt and then combine the mixture with your hands.
3) In the bowl of an electric mixer fitted with the paddle attachment, beat the brown sugar, oil and treacle on medium speed for 5 minutes. Turn the mixer to low speed, add the egg, and beat for 1 minute.
4) Scrape the bowl with a rubber spatula and beat for 1 more minute. With the mixer still on low, slowly add the dry ingredients to the bowl and mix on medium speed for 2 minutes. Add the crystallized ginger and mix until combined.
5) Scoop the dough with 2 spoons or a small ice cream scoop. With your hands, roll each cookie into a 4.5cm ball and then flatten these lightly with your fingers. Press both sides of each biscuit in caster sugar and place them on the sheet trays.
6) Bake for exactly 13 minutes. The biscuits will be crackled on the top and soft inside. Let the biscuits cool on the trays for 1 to 2 minutes, then transfer to wire racks to cool completely.