Beat the butter for two minutes in a kitchen machine.
Add the egg, sugar, bourbon vanilla sugar and salt and beat until pale.
Stir in the flour until you have a smooth dough.
Form the dough on a well-floured working surface to a long roll with a diameter of 5cm/2in. Wrap the roll in a baking paper and let it chill for one hour in the fridge. Cooling the dough makes it easier to cut it later.
Preheat your oven to 200°C/390°F (conventional).
Place your chilled dough-roll on a cutting board and cut about 1cm/0.4in thick cookies. Put them on a with baking paper lined baking sheet. The cookies should have enough space. Therefore it's better to use two baking sheets.
Bake your cookies for 10 minutes in the middle of the preheated oven. If you use two baking sheets, bake one after the other.
Let them cool down on a cooling rack.
You can store your butter cookies with the pastel glaze up to one week in a cookie box.