Line your baking dish with parchment paper, leaving some overhang for easy removal. This makes lifting out the slice a breeze once it's set.
Chop the dark chocolate into small, even pieces and set aside.
In a saucepan over low heat, melt the butter and dark chocolate together, stirring gently. You'll notice a shiny, smooth mixture forming as the chocolate fully melts and combines with the butter.
Remove the saucepan from heat and stir in the sweetened condensed milk until the mixture is silky and well blended, with a rich aroma filling your kitchen.
In a separate bowl, crush the digestive biscuits into coarse crumbs—some small pieces are fine, just avoid over-mashing for texture.
Fold the crushed biscuits into the chocolate mixture until evenly coated, creating a thick, fudgy batter.
Pour the mixture into your prepared dish, then use a spatula to spread it out evenly and press down gently to compact everything nicely.
Optional: sprinkle a pinch of sea salt or chopped nuts over the top for added flavor and crunch.
Refrigerate the slice for at least 3 hours, or until it’s firm and shiny on top. Cover with plastic wrap if desired to prevent any fridge odors from seeping in.
Once set, lift the slice out using the parchment paper overhang and transfer it to a cutting board. Use a sharp knife to cut into squares or rectangles, wiping the blade clean between each cut for neat edges.
Serve your luscious chocolate slices immediately, or store leftovers in an airtight container in the fridge for up to three days. Enjoy the rich, melt-in-your-mouth texture with every bite!
