Line a quarter sheet pan (13x9-inch) with parchment paper. Be sure to leave enough parchment paper overhanging the sides to easily lift the chilled peppermint bark from the pan once set.
In a microwave safe glass bowl, melt the finely chopped semi-sweet chocolate for 1 minute, then heat in 1 to 2 more 30 second intervals (being sure to stir the chocolate between each heating interval) just until most of the chopped chocolate is melted. A few small pieces of chocolate that are not fully melted are fine, as they will continue to melt as the chocolate is stirred.
Add ½ teaspoon peppermint extract to the melted semi-sweet chocolate and stir to a smooth consistency.
Spread the melted semi-sweet chocolate into an even layer in the prepared pan.
Sprinkle ⅓ cup of the crushed candy canes evenly over the melted semi-sweet chocolate layer. Place the pan into the refrigerator for 10-15 minutes or just until the chocolate is just starting to set. The chocolate should still be a little tacky to the touch (leaving a fingerprint in the chocolate but not pressing all the way through) to help ensure the white chocolate layer adheres properly and does not separate once fully chilled, set, and broken into serving pieces.
During the last 3-4 minutes of the chill time for the semi-sweet chocolate layer, add the chopped white chocolate to a separate microwave safe bowl and heat for 1 minute. Stir, then heat in 30 second intervals (stirring between each interval) until most of the white chocolate chunks have melted. Add the remaining ¼ teaspoon peppermint extract and stir until smooth.
Remove the pan from the refrigerator, pour the melted white chocolate over the slightly set semi-sweet chocolate layer spreading to fully cover the first layer of chocolate and crushed candy canes. A small offset spatula works well to quickly and evenly smooth the white chocolate layer.
Top the melted white chocolate evenly with the remaining ⅓ cup crushed candy canes. Refrigerate the peppermint bark for an additional 45-60 minutes or just until fully set.
Remove the chilled peppermint bark from the refrigerator and carefully lift it out of the pan using the overhanging parchment paper. Break the bark into about 2 to 2½-inch sized pieces with your hands or use a large sharp knife to cut the bark into more uniform sized square pieces.
Serve the bark immediately or place into an airtight container and store at room temperature for up to 2 weeks.
Notes
Using a high quality brand of chocolate baking bars is essential in this recipe as the chocolate will melt more smoothly and set up much better once chilled. Ghirardelli and Lindt brands are most commonly found at traditional grocery stores either in the baking or candy aisle.
If using Lindt brand white chocolate bars, they come in a 4.4-ounce sized bar. Either the 4-ounce Ghirardelli brand or the 4.4-ounce Lindt brand bars will work just fine as this is a forgiving recipe for an easy homemade peppermint bark. If using the Lindt brand, you will need four 4.4-ounce white chocolate bars finely chopped. There will be no need to adjust any of the other ingredient amounts in the recipe.
When choosing both the semi-sweet and white chocolate baking bars, be sure to choose a brand that does not contain palm oil as this ingredient may cause the layers to separate once the peppermint bark has chilled and set.
Do not use semi-sweet or white chocolate chips as they contain emulsifiers and other ingredients that can cause the peppermint bark to separate once chilled. These added ingredients can also hinder the chocolate from melting smoothly when heated in the microwave.