Line your pan with parchment paper, leaving overhang to make removal easier.
Chop the dark chocolate into small pieces to help it melt evenly.
Place the chocolate in a microwave-safe bowl and melt it in 30-second bursts, stirring after each, until smooth and glossy.
While the chocolate melts, toast the mixed nuts in a dry skillet over medium heat until fragrant and lightly golden, about 3-4 minutes. Let them cool slightly.
Add the butter and honey to the melted chocolate, stirring until fully combined and the mixture is warm and inviting smelling.
In a large bowl, combine the toasted nuts and oats, if using.
Pour the warm chocolate mixture over the nuts and oats, folding gently with a spatula until everything is evenly coated and sticky.
Transfer the mixture into your prepared pan, pressing down firmly and evenly with the back of a spatula to create a compact, smooth surface.
Refrigerate for at least 2 hours, or until the chocolate is firm and slices cleanly. For quicker setting, pop it in the freezer for about 1 hour.
Once set, lift the slice out of the pan using the parchment overhang, and cut into squares with a sharp knife, wiping the blade between cuts for clean edges.
Serve immediately or store in an airtight container in the fridge. Enjoy the rich, crunchy texture with every bite!
