In a large bowl, cream the butter and sugar using a stand or hand mixer. Whip the butter until pale and fluffy. Add the egg, salt and vanilla then beat again on high speed for around 1 minute.
Separately, sift together the flour, baking powder and nutmeg. Add the flour into the butter mixture and mix on low speed until a dough forms. If the dough seems too soft to roll, sprinkle in 1 tablespoon of flour. Cover the cookie dough with plastic wrap, then refrigerate for 1-2 hours or overnight.
Pre-heat the oven to 350°F and line two large baking sheets with parchment paper.
Flour the worksurface, then roll out the dough using a rolling pin. If the dough is too sticky when rolling, sprinkle more flour onto it. The thickness should be ¼ inch.
Using a 2-inch round cookie cutter, cut out 24 circles. Use a small cookie cutter or the back of a piping nozzle to cut out ½ inch holes in the middle.
Place the cookies on the baking sheets, at least 2 inches apart. Bake for 11-12 minutes or until golden-brown on the edges.
Once baked, let cool for 5 minutes on the sheets, then transfer to a cooling wire to cool completely.
Royal icing:
Combine the egg white and powdered sugar with the help of a hand mixer.
Add in the lemon juice a few drops at a time, until the mixture reaches the desired consistency.
Divide the icing into 4 separate containers. Leave one white, the color the other three in yellow, green, and purple.
In a separate bowl, place dollops of white icing. On top, place small dots of colored icing.
Dip each cookie face down into the icing, then lift and let the excess drop off. Place the cookies on a wire rack to harden.
If the colors become too merged, place more white icing on top to create a white canvass. Repeat the process with small dollops of colorful icing on top of the white.
Optional: sprinkle some edible glitter on top whilst the icing is drying.
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