Preheat the oven to 350 degrees F.
Line a baking sheet with parchment paper or a silicone mat. Set aside.
In a large bowl, beat the butter until fluffy.
Add the sugar and salt and beat until well combined and fluffy.
Beat in the egg and the vanilla until well combined.
Gradually add the flour and beat until completely mixed but not overworked.
Add the food coloring and peppermint extract to the cookie dough and mix very well.
Roll the dough into balls and place them on the prepared baking sheet.
Lightly press down on top of each cookie ball using a flat bottom of a glass dipped in water.
Sprinkle the tops lightly with granulated sugar if desired.
Bake for 8-10 minutes or until the edges are set.
Remove and allow to cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.
Melt the chocolate in a microwave-safe bowl.
Crush the peppermint candies in a resealable bag using a rolling pin.
Dip the edge of each cookie into the melted chocolate and then immediately sprinkle on the crushed peppermint candies before the chocolate has set.
Place the cookies on a wire rack until set.
Store in an airtight container at room temperature.