2) Beat the butter in a large bowl with a handheld mixer until fluffy. Scrape down the sides of the bowl add the sugars and continue beating until light, about 3 mins. Add egg and vanilla essence, beating until smooth. Gradually add the dry ingredients while mixing slowly to make a smooth dough.
3) Divide the dough in half and press each half into a disk. Wrap in cling film and refrigerate until firm, at least 1 hr.
4) Transfer 1 disk of dough to a floured work surface and roll out about 0.5cm thick. Cut into biscuits with a pinched tuna can (see below). Transfer the biscuits with an offset spatula to a nonstick or silicon-lined baking tray.
5) Cut out eyes and a mouth with a pastry tip, fat straw or a knife. Press a lollipop stick into the narrow end of each biscuit, if using. Repeat with the remaining dough. Press any excess dough together, roll and cut into biscuits. Refrigerate the biscuits for at least 30 mins.
6) Evenly space the racks in the oven and preheat the oven to 180C/Gas 4. Put the sweets in a small plastic bag and hit with a rolling pin to break into small pieces.
7) Bake the biscuits just until they are set, about 20 mins. Remove the baking trays from the oven and carefully sprinkle the broken sweets into the eyes and mouth of the cookies. Continue to cook until the sweets liquefy, about 3 mins more. Cool the biscuits on the trays for 10 mins before removing onto a rack.
For the icing:
1) Whisk the water, egg white powder and orange essence in a medium bowl until foamy but smooth. Gradually whisk in the icing sugar to make a smooth icing. Spread a layer of icing over the entire surface of the cookies with the back of a teaspoon. Leave to rest until the icing sets, about 30 mins. Serve or store in a covered container for up to 3 days.
Cook's Note: Remove the top and bottom of the tuna can and discard. Wash and dry well. Pinch the sides of the can together at one end to make a skull-like shape.