Place the soft butter and white sugar into a mixing bowl.
With a sharp knife, split the vanilla bean lengthways down the middle and scrape the seeds into the bowl of butter and sugar.
Place the pod into the cup of white sugar for rolling. Stir and cover and leave for the vanilla to infuse in the sugar, while you prepare the cookie dough.
Add the vanilla extract to the bowl of butter, sugar, and vanilla bean seeds, and beat with an electric handheld or standing mixer until smooth and creamy.
Beat in the powdered sugar until smooth.
Add the egg to the mixture and beat until the dough is fluffy.
With a rubber spatula, mix in a pinch of salt and the flour until it is incorporated and a dough forms.
Place two lengths of plastic wrap onto your work surface.
Divide the dough in half and place one half onto each piece of plastic wrap.
Wrap the dough and work into a log. Twist the ends to secure and place the dough into the freezer (20 minutes) or fridge (1 hour) to firm up. Both ways work great, just use the method that fits with your available time.
When you are ready to bake, preheat the oven to 325°F/170°C/Gas 3. Prepare a cookie sheet with nonstick spray or parchment paper.
Unwrap the chilled cookie dough logs and cut them into ¼"/½cm slices with a sharp knife.
Uncover the vanilla bean sugar and place each cookie slice, one at a time into the sugar to coat it completely.
Place the cookies onto the prepared cookie sheet about 2"/5cm apart.
Bake for 17-20 minutes until the edges are slightly golden brown.
Leave cookies to cool for 10 minutes on the cookie sheet then transfer them to a wire rack to cool completely before enjoying them with a glass of milk!