Special equipment: a 4 1/2-inch star or snowflake shaped cookie cutter; a 1 1/2-inch star cookie cutter; a wooden skewer, optional
Preheat the oven to 400 degrees F. Line two baking sheets with parchment paper.
Heat the butter, sugar, golden syrup, treacle, ginger, cinnamon, cloves and chili powder, if using, in a saucepan until the butter melts and the sugar has dissolved.
Remove the pan from the heat and stir in the flour and baking soda. You should have a smooth but fairly stiff dough. Chill for 5 minutes (it¿s important to work with the dough while it is still a little warm as it becomes quite dry and crumbly upon cooling completely).
Roll the dough out to a 1/2-inch thickness on a large sheet of parchment paper. Use a 4 1/2-inch star or snowflake cookie cutter to cut out the cookies. Use a 1 1/2-inch star cutter to stamp out the center of each cookie.
Use a palette knife to lift the large stars onto a baking sheet. To make decorations, use a wooden skewer to make a hole in the top of each cookie. Re-roll the remaining dough and the leftover smaller stars and continue to make the cookies in this way until all the dough is used up.
Place a little of the ground hard candy in the center of each star, using a separate color for each cookie.
Bake in the oven until the cookie is crisp and beginning to darken and the hard candy has melted to fill the hole, 8 to 10 minutes. Remove from the oven and use the wooden skewer to make sure the holes are intact.
Leave to cool completely, then slide a palette knife under each cookie to release them from the paper.
Pipe or drizzle the royal icing onto the cookies.
Golden syrup (also called pale treacle) and black treacle are sweet byproducts of the sugar refining process and are popular in British cooking. You can find them at some specialty food stores and online markets.