Preheat oven to 350ºF. Line an 8-inch or 9-inch square baking pan with parchment, pray with nonstick cooking spray or grease with butter. Sprinkle crushed pretzels evenly in the bottom of the pan. Set aside.

In a large bowl, combine the melted butter and the sugars and stir until completely combined. Beat in egg and vanilla.

Stir in the flour, salt, baking powder, and baking soda. Once combined, gently fold in the white chocolate chunks and 1/2 cup Andes peppermint chips.

Press the dough evenly into the prepared baking pan. Bake for 25-26 minutes or until very lightly browned on top. You want the cookie bars to be soft, so careful not to overbake. Allow the bars to cool completely.

Spread with melted white chocolate and sprinkle with remaining 1/2 cup Andes peppermint chips and more pretzels, if desired. Let chocolate cool. Cut, and serve.

Store bars in an airtight container at room temperature for up to 2 days and in the refrigerator up to 5.