Preheat the oven to 180 degrees Celsius and line two baking trays with parchment paper.
In a bowl, cream together the softened butter and sugars until fully combined.
Add the egg and mix thoroughly.
Incorporate the chocolate chips into the mixture.
Sift in the flour, dark cocoa powder, and baking powder. Mix until well combined.
Roll the dough into balls with your hands and place them on a lined baking tray.
Bake in the preheated oven for 10-12 minutes.
Once cooked, allow the cookies to cool and harden on the tray.
Melt the chocolate and transfer it to a piping bag, cutting the end to create a small hole.
Pipe melted chocolate onto the back of pretzels and attach two to the top of each cookie to resemble reindeer antlers.
Pipe a small amount of chocolate onto the backs of red Smarties and candy eyes, placing them on the cookies to create a face. Allow it to set.
Enjoy your festive reindeer cookies!