Chop the dark chocolate into small pieces and set aside.
In a saucepan over low heat, melt the chocolate gently, stirring constantly until smooth and shiny, and you can smell the rich cocoa aroma.
Add the butter to the melted chocolate and stir until completely melted and glossy, creating a silky mixture.
Pour the warm chocolate-butter mixture into a large mixing bowl, then stir in the vanilla extract to brighten the flavor.
Add the crispy cornflakes to the bowl and fold gently with a spatula, coating each flake evenly while keeping them crispy.
Transfer the coated cereal mixture into a lined or greased baking dish, pressing down firmly with the back of the spatula to create an even, compact layer.
Let the mixture set at room temperature for about 30 minutes, or refrigerate for 15-20 minutes until the chocolate is firm and the bars hold their shape.
Once cooled and firm, use a hot, damp knife to cut into squares or rectangles, wiping the knife clean after each cut for neat edges.
Allow the bars to rest for a few minutes after cutting to firm up before serving. Enjoy these rich, crunchy treats as a quick snack or dessert.
