Line a baking sheet with parchment paper and set it aside.
In a medium saucepan, combine the butter, sugar, and cocoa powder. Heat over medium-low, stirring constantly, until the butter melts completely and the mixture turns glossy and smooth, about 2 minutes. You’ll notice it bubbling gently and smelling rich and chocolatey.
Increase the heat slightly and bring the mixture to a gentle boil, letting it bubble for exactly 1 minute. This helps the cookies set properly and develop that sticky, glossy texture.
Remove the saucepan from heat and stir in the vanilla extract. Then, gently fold in the cornflakes, mixing carefully so they stay as crispy as possible and are evenly coated with the syrup. You'll see the flakes glisten and stick together slightly, but still retain their crunch.
Using a spoon, scoop generous dollops of the mixture onto your prepared baking sheet. Gently flatten each mound with the back of the spoon to shape the cookies and help them set faster. The mixture should be sticky but manageable.
Let the cookies sit at room temperature for about 15 minutes, allowing the coating to firm up slightly. Then, transfer the tray to the fridge and chill for at least 30 minutes until they are completely set and firm to the touch.
Once chilled and firm, remove the cookies from the fridge. They will have a shiny, crispy exterior with a chewy interior—perfect for snacking or sharing. Serve straight from the fridge or at room temperature for a delicious nostalgic treat.
