In a large bowl, beat the butter, sugar and salt until smooth and well combined. Beat in the egg and vanilla until incorporated. Mix in the flour just until combined.

Form the dough into a disk and wrap it with plastic wrap. Chill it in the refrigerator until firm, at least 2 hours or overnight.

Preheat the oven tp 350ºF (180ºC). Line 2 large cookie sheets with parchment paper.

On a lightly floured surface (or between parchment sheets), roll the dough to 1/4-inch thickness. Cut out 18-20 star shapes using a 4-inch cookie cutter.* Place the stars about 2 inches apart onto the cookie sheets. Cut the center out of each star using a 2-inch cookie cutter.* Place the small star cut outs on a separate cookie sheet. Sprinkle with sanding sugar. Fill the cut out section of the large stars with the crushed butterscotch candy. I recommend chilling the cut cookies in the refrigerator for 15-20 minutes to prevent excess spreading.

Bake until the candy melts and the edges of the cookies start to turn light golden brown, about 8-10 minutes. Let the cookies cool on the cookie sheet. Bake the small stars for 6-8 minutes. Transfer them to a cooling rack.