Line a baking sheet with parchment paper, ensuring it lies flat without wrinkles.

Melt the dark chocolate in a double boiler or microwave, stirring frequently until smooth. Stir in 1/4 tsp peppermint extract.

Pour the melted dark chocolate onto the prepared baking sheet. Use a spatula to spread it evenly into a thin layer. Let it cool for 10 minutes.

Melt the white chocolate in a double boiler or microwave, stirring frequently until smooth. Stir in the remaining 1/4 tsp peppermint extract.

Pour the melted white chocolate over the cooled dark chocolate layer. Spread it evenly with a spatula.

Immediately sprinkle the crushed peppermint candies and sea salt (if using) over the white chocolate layer. Gently press them in with your hands.

Let the bark cool completely at room temperature or in the refrigerator for about 1 hour until firm.

Once set, break the bark into pieces by hand or cut it with a sharp knife. Serve or store in an airtight container.