Cream the butter and sugar together in the bowl of an electric mixer on low to medium speed. (Use the paddle attachment). Mix until thoroughly incorporated - for about one minute. Scrape down the sides of the bowl with a plastic spatula and mix again for a few seconds more. Over mixing the butter and sugar in this step will cause too much air to be incorporated into the dough. If you'd like a light and fluffy cookie, that's ideal, however the dough will spread more during baking; not ideal if you'd like the cookie to hold its shape.
Add ground nutmeg and mix.
Add eggs slowly and mix. Scrape down the bowl with your spatula at least once and mix.
Whisk your dry ingredients together. (Flour and salt, and baking powder if you're using it).
Add all of the flour mixture to the bowl. Place a large tea towel or two small tea towels between the edge of the bowl and the electric mixer so that the flour won't escape. Mix on low speed for 30 seconds. Remove the tea towels and observe the dough mixing; when it clumps around the paddle attachment it's ready. It's also important at this stage not to over mix the dough (the gluten in the flour develop and the dough can become tough).
Roll the dough out between 2 large pieces of parchment paper. Place on a baking sheet and into the fridge for a minimum of 1 hour.
Cut out cookie shapes. Place on parchment paper-lined baking sheet. Re-roll scraps and repeat.
Put cookie dough shapes back into the fridge for 10 minutes to 1 hour to chill again. They will then hold their shape better when baked.
Preheat your oven to 350°F or 176°C.
Bake cookies for 8-12 minutes or until the edges become golden brown. The baking time will depend on the size of your cookie.
Let cookies cool to room temperature and decorate!