Place a wire baking rack or piece of wax paper over a baking sheet. Open the boxes of shortbread and remove the cookies from the packaging.
Melt the white chocolate chips by placing them in a glass bowl set over a pot of simmering water. Use a spatula to stir the chips until melted. Remove from heat. Submerge a piece of shortbread halfway into the melted chocolate, then allow any excess chocolate to drip off of the cookie back into the bowl. Hold the chocolate-coated cookie over the baking rack or wax paper, then sprinkle crushed macadamia nuts onto the chocolate coating. Place on the baking rack to set; repeat with 7 more cookies (one box total).
Melt the dark chocolate by placing the chips in a microwave-safe bowl and heating for 15 seconds at a time in the microwave, stirring with a spatula in between heating intervals. Once melted, repeat the dipping and coating process with the second box of shortbread (8 cookies) and the sliced almonds.
Melt the milk chocolate chips in the microwave using the same method, then proceed to coat the remaining 8 cookies with milk chocolate and top with pretzels.
Notes
To store biscotti, place them in an airtight container at room temperature for up to two weeks. For longer storage, put it in a freezer-safe bag and you can store it for up to 3 months.To reheat, preheat your oven to 300 degrees F (150°C) and bake the biscotti for 5-10 minutes until warm and crisp.