Leave the butter at room temperature before starting to bake. Use the paddle attachment to mix the butter, powdered sugar, cornstarch until smooth and silky.
1 cup Butter, ¾ cup Powdered sugar, ¼ cup Cornstarch
Add the egg yolk and vanilla extract.
1 Egg yolk, 1 teaspoon Vanilla extract
Mix the flour, cinnamon, and salt, add it in two or three passes, and mix well after each. You would have a soft and smooth dough in the end.
2½ cup All-purpose flour, ½ teaspoon Salt, 1 teaspoon Cinnamon
Shape the dough into a disc, cling wrap, and chill for one hour.
Lightly flour a clean surface and roll out the dough. For easier rolling, place the dough between two pieces of wax paper. Once the dough is ¼ of an inch thick, use your snowflake or any holiday cookie cutter to cut the dough.
Place the raw cookies on a lined baking sheet and in the fridge for 15 to 20 minutes.
In the meantime, preheat the oven to 325F. Bake the cookies for 8-10 minutes or until the edges look set. Do not overbake them, as it makes them dry and brown. Let them cool down for a few minutes, then transfer them to the cooling rack to cool down fully.