Line a large baking sheet with parchment paper or a silicone mat and set aside.
Melt the dark chocolate in a double boiler over simmering water, stirring frequently until smooth and completely melted. Alternatively, microwave in 30-second intervals, stirring between each, until fully melted.
Pour the melted chocolate onto the prepared baking sheet and use an offset spatula to spread it into a rectangle about 1/4-inch thick, keeping the edges slightly irregular for a rustic look.
Let the chocolate sit at room temperature for 5 minutes until it begins to set but is still slightly tacky to the touch.
Meanwhile, combine the caramel candies and heavy cream in a small microwave-safe bowl. Microwave in 20-second bursts, stirring between each, until smooth and pourable. Stir in the vanilla extract if using.
Drizzle the warm caramel over the chocolate in thin ribbons, using a spoon or fork to create a swirled pattern. Work quickly before the caramel firms up.
Immediately sprinkle the flaky sea salt evenly over the top, focusing on areas where the caramel ribbons are visible.
Let the bark set at cool room temperature for 2-3 hours until completely firm and cool to the touch. Once set, break into irregular pieces by hand and serve or store in an airtight container.
