Preheat oven to 325 degrees F. Grease an 8-inch round baking dish. I used a tart pan with removable sides. You can also use an 8-inch square dish.

With an electric mixer, beat the butter and sugar until smooth and creamy, 2-3 minutes. Mix in the peppermint extract.

Add the flour and salt and mix until just incorporated.

Press the mixture into your prepared pan. Bake just until top starts to turn golden brown, 30-35 minutes. If you use a square baking dish, check at 25 minutes.

Let cool completely.

In a heat-proof bowl set over a pot of simmering water, or in the microwave in 30 second bursts, melt the semi-sweet chocolate and 1 tablespoon of the heavy cream together until smooth. Be careful not to overheat and burn. Stir in 1/2 teaspoon of the peppermint extract. Spread over the cooled shortbread. If desired, reserve some of the melted chocolate to drizzle on top. Chill in the freezer until firm, about 5 minutes.

Melt the white chocolate and remaining 1 tablespoon of the heavy cream together until smooth. Stir in remaining 1/2 teaspoon of the peppermint extract. Spread on top of the semi-sweet chocolate.

Drizzle with remaining melted chocolate, if you set some aside. Sprinkle with crushed candy canes. Chill in the freezer until firm, 5-10 minutes.

For clean slices, heat a sharp knife by running it under hot water and wiping clean with a towel. Re-heat as needed.

For best results, store shortbread in the fridge.