Directions:

"Making the Dough:
Put all dough ingredients into a large bowl.
Mix the ingredients by hand or mixer until you have a nice dough.
Shape the dough into a somewhat flat rectangular shape, cover it (i.e. with beeswax cloth in silicone bag or container) and put it into the fridge.
Let the dough rest for at least 6 hours or overnight, then continue with making the icing.

Make the Royal Icing:
Prepare the icing: For a perfect icing, weigh the egg whites and use 5 times this weight for the confectioner's sugar.
Start by mixing the egg whites.
When the egg whites are fluffy and shiny, add ⅓ of the confectioner's sugar and mix.
Repeat until the entire sugar is in the icing.
Put the icing in a bag, ideally a piping bag, but ziploc works!

NOTE: if the icing dries too quickly just wet your finger or just add a small amount of water to make it liquid again

Baking:
Take the dough out and roll out to about 1/4 in thick slab and cut into whatever shape (small stars is the traditional shape)
Ice the cookies however you'd like, traditionally it's a flat layer/finish that covers every edge

*Optional* Leave the cut cookies out to dry for 2 hours before baking (my family skips this to get more moist cookies)

Preheat the oven to 180°C / 350°F (a little lower than in the video) and bake for about 8 minutes. Try to set the cookies on the lowest shelf so as not to burn the royal icing so quickly
You know that the cinnamon stars are ready when you can lift them from the baking sheet.
Don't let the royal icing bake to a tan.
Let the cookies cool, then store them in an airtight container."