Preheat your oven to 180°C (350°F) and line your baking pan with parchment paper, leaving some overhang for easy removal.
Spread the sliced almonds evenly on a baking sheet and toast in the oven for about 8-10 minutes until golden and fragrant. Keep an eye on them to prevent burning, then set aside to cool.
Once cooled, roughly chop or leave the almonds as is for a more rustic look. Melt the dark chocolate and butter together in a microwave-safe bowl, heating in 30-second bursts and stirring until smooth and glossy.
Gently fold the toasted almonds into the melted chocolate mixture, ensuring they are evenly coated. Pour this mixture into your prepared pan, spreading it out smoothly with a spatula.
Sprinkle a few extra toasted almonds on top, pressing them lightly into the chocolate to ensure they stick and add a crunchy topping.
Chill the bars in the fridge for at least 2 hours, or until the chocolate is firm and set. For quicker results, you can freeze them for about an hour.
Once set, lift the bars out of the pan using the parchment overhang and place on a cutting board. Use a sharp knife to cut into even squares or rectangles.
Finish by sprinkling a tiny pinch of flaky sea salt over each piece for extra flavor contrast.
Serve immediately for a satisfying crunch and rich flavor, or store in an airtight container in the fridge for up to a week. Let them sit at room temperature for about 10 minutes before enjoying for the best texture.