Gather all your ingredients and line a baking sheet with parchment paper to prepare for setting the cookies.
In a saucepan over low heat, melt the butter gently, stirring occasionally until it’s smooth and glossy, and you can smell the rich aroma of butter filling your kitchen.
Add the semi-sweet chocolate chips to the melted butter. Stir continuously until the chocolate is fully melted and the mixture becomes silky and shiny, about 2-3 minutes.
Stir in the sweetened condensed milk and vanilla extract, mixing well until everything is combined into a smooth, glossy sauce with a sweet aroma.
Remove the pan from heat and gently fold in the cornflakes, tossing carefully to coat each flake evenly with the chocolate mixture, avoiding crushing the cereal.
Using a tablespoon or small scoop, drop spoonfuls of the mixture onto the prepared parchment-lined baking sheet, leaving about two inches of space between each cookie.
Let the cookies sit at room temperature for 30-60 minutes, allowing the chocolate to set and the cookies to become firm with a shiny, crackly surface.
Once set, gently peel the cookies off the parchment paper and transfer them to a plate or container. Enjoy these crunchy, gooey treats that require no baking!