Preheat the oven to 350°F. Line your baking sheets with parchment paper. Set aside.
In the bowl of a stand mixer, combine the butter and sugar. Cream until smooth.
Add in the egg, milk, and vanilla. Mix until smooth.
Add in the flour and salt and mix thoroughly. Stop the machine, scrape down the sides, and mix again.
Transfer the dough to a piping bag fitted with a large star tip. Pipe small spirals on your parchment-lined baking sheets. Allow to chill in the freezer for 10 minutes.
Bake in the preheated oven for 10-12 minutes or until no longer shiny and the edges are set.
Allow to cool completely before removing from the parchment.
Place the chocolate in a microwave-safe dish and heat in 30-second increments, stirring well between each interval until smooth. Repeat with the white chocolate. Be careful not to overheat as the chips can scorch easily.
Lift each cookie off the parchment and hold it on one edge. Dip about ½ of the cookie in the melted chocolate. Place back on the parchment and decorate with the sprinkles.
Repeat with the remaining cookies using both the chocolate and white chocolate.