In a small mixing bowl, whisk together the flour and salt. Set aside.
In a large mixing bowl or in the bowl of a stand mixer, beat the room temperature butter for about 3 minutes until it is creamy and a paler yellow.
Add the sugar to the butter and beat for another 3 minutes, until it is fluffy and very pale yellow.
Add in the egg and vanilla extract. Beat for another minute or two, until the egg and vanilla are fully incorporated.
Add half the flour and salt mixture and beat on a low speed for about a minute, until there is no dry flour visible.
Add the remaining half of the flour and salt mixture and beat for another 3 minutes, until there is no more dry flour visible and the dough stays in a ball when you squeeze it in your palm.
Divide the dough in half and shape the dough into two round discs. Wrap them individually in plastic cling wrap and refrigerate for at least 2 hours or up to 2 days.
When you're ready to begin rolling out the dough, take the dough out of the fridge for at least 15 minutes, so it can warm up a bit and become easier to work with.Preheat the oven to 350°F. Line a baking sheet with parchment paper or a siplat. On a lightly floured clean work surface, roll out one of the dough discs until it is ¼-inch thick.
Cut out shapes with your cookie cutters.
Spread out the cookies on the baking sheet and bake for 10 to 12 minutes, until they are golden around the edges.
Transfer the cookies to a wire rack to cool.Continue rolling out the dough and cutting cookie shapes until you've used all the dough.Let all the cookies cool completely before decorating them.