Preheat your oven to 350°F (175°C). Line a large baking sheet with parchment paper and set it aside.
In a large bowl, cream the softened butter and granulated sugar together until smooth. Add the eggs one at a time, mixing well after each addition. Stir in the peppermint extract.
In a separate bowl, whisk together the flour, baking powder, kosher salt, and half of the crushed peppermint candies.
Gradually add the dry ingredients to the butter mixture. Stir until just combined. The dough will feel sticky.
Divide the dough in half. Place both halves on the prepared baking sheet. Shape each piece into a 12-by-2.5-inch rectangular log, leaving a few inches of space between them to allow for spreading. Ensure the center of the dough reaches a safe internal temperature of 160°F (71°C) during baking.
Bake for 25 to 30 minutes, or until the logs are light golden brown. Remove from the oven and let cool on a wire rack for exactly 15 minutes.
Transfer the warm logs to a cutting board. Using a sharp knife, cut diagonally into 1/2-inch thick slices. Place the slices cut side down on two parchment-lined baking sheets.
Bake the slices for 12 to 15 minutes until firm. Transfer the biscotti to wire racks to cool completely.
Melt the chocolate chips in a heatproof bowl set over a pot of simmering water. Dip one end of each cooled biscotti into the chocolate. Sprinkle with the remaining crushed candies and set on parchment paper until the chocolate hardens.