Line a large baking sheet with parchment paper or a silicone mat. Set aside.
Place the chopped dark chocolate in a microwave-safe bowl. Microwave in 30-second intervals, stirring thoroughly after each burst, until melted and smooth. This usually takes 90 seconds to 2 minutes total.
Let the melted chocolate cool for 2-3 minutes, stirring occasionally, until it's no longer steaming but still pourable.
Pour the chocolate onto the prepared baking sheet and use a spatula to spread it into an even layer about 1/4 inch thick. Work quickly before it begins to set.
Immediately sprinkle the flaky sea salt evenly over the surface. If using optional toppings, scatter them now and press gently with your fingers to help them stick.
Refrigerate the bark for 15-20 minutes, or until completely firm and set.
Remove from the fridge and break the bark into irregular shards by hand or cut into squares with a sharp knife. Store in an airtight container.
