Preheat oven to 180°C / 356°F.
Cut butter in small pieces and add to your electric mixer's bowl, along with the 200 grams of icing sugar, orange zest, vanilla extract, and nutmeg.
With the whisk attachment on, beat over low speed for 2-3 minutes and then raise the speed to medium. Beat for about 5 minutes, or until the butter looks very creamy and airy.
Reduce heat to low and add the eggs, the milk, and the brandy (or scotch).
Once fully combined, add the baking powder and the flour in small bits at a time.
Raise heat to medium again and beat for 2-3 minutes more until everything combines well.
Grease a springform cake pan (23 cm / 9 inch round) and add the batter. Spread evenly using a silicone spatula.
Bake for about 20-25 minutes. Prick the center with a knife and make sure it comes out clean.
Let cake reach room temperature and then remove from pan.
If the cake has risen unevenly slice off with a knife. Place the coin inside the cake.
Flip the cake in order to face its bottom and place it on a serving plate or cake stand.
Dust with plenty of icing sugar (make sure the cake has cooled completely before doing this).
Take a piece of parchment paper and lay it on top of the cake. With your hands gently caress the parchment paper making the icing sugar below to stick together and become smooth.
Carefully remove the parchment paper.
Melt the chocolate either in a double boiler or in your microwave for 2-3 minutes on medium heat. Make sure you stir every 30 seconds so it won't burn. Transfer chocolate in a piping pen and decorate the cake by writing a Happy New Year or the New Year's number.
Let the chocolate cool and you're ready to serve!