Preheat oven to 180C. Line 4 baking trays with baking paper.
Make the cookies: In a mixer add the softened butter and muscovado sugar, and beat together until light and fluffy. Next add the eggs and mix again. Then sift in the flour, baking powder and salt and add the vanilla essence and mix thoroughly until it forms a firm dough. Tip this out onto a floured surface and roll your dough out to approximately ½ cm thick. Chill for 10 minutes.
Using either a star or a circular cutter, cut out 40 cookies. Place 10 cookies onto a baking tray as they are. With the other 30, using the same cutter but a smaller size, cut a window in the middle of each. Place 10 of these cookies onto a baking tray and in the middle of each, place either one red boiled sweets or one green boiled sweets. With the remaining 20 cookies, simply place them on the baking trays. Bake all of the cookies for approximately 10 minutes, until lightly golden brown, and the boiled sweets have melted in the window cookies.
Remove from the oven and allow them to cool completely.
Make your candy cane filling
Make your white icing by adding a tbsp of water to your icing sugar and mixing well. Place in a piping bag and cut a very small nozzle. Take your candy canes and place them in a ziplock bag, then bash them with a rolling pin until you have small pieces.
Assemble your cookies: Take your cooled cookies and start with the one without a hole in the middle. Using your icing, pipe a thin line around the outside of this cookie without going too near to the edges. Now place a cookie with a hole on top, making sure the edges line up. Repeat this with the next cookie with a hole. At this point, fill the cavity in the middle with your crushed candy cane pieces. Finally, seal the top cookie with the red or green window on the top with your icing. Repeat with all your cookies and then allow them to set up. Finally dust with extra icing sugar.
Have fun smashing your cookies and revealing the candy cane surprise!