Line your baking dish with parchment paper, leaving some overhang for easy lifting.
In a saucepan over low heat, melt the butter and dark chocolate together, stirring gently until smooth and glossy, filling your kitchen with a rich, chocolatey aroma.
Remove the saucepan from heat and stir in honey or maple syrup, along with vanilla extract, until well combined and the mixture feels smooth and slightly thickened.
In a large mixing bowl, toss the oats and a pinch of salt together, ensuring they’re evenly distributed.
Pour the melted chocolate mixture over the oats and stir vigorously with a spatula until everything is thoroughly coated and sticky, with a glossy sheen.
Transfer the mixture into your prepared dish, pressing it down firmly with the back of a spatula or a glass to create an even, compact layer about 1.5 inches thick.
Place the dish in the fridge and chill for at least 2 hours, or until the mixture is firm and shiny, with a chewy, dense texture.
Once set, lift the bars out of the dish using the parchment overhang and transfer to a cutting board.
Use a sharp serrated knife to cut into even squares or rectangles, wiping the knife clean between cuts for neat edges.
For a polished look, sprinkle lightly with sea salt flakes or dust with cocoa powder, then serve immediately or store in an airtight container in the fridge.
