01 - Line an 8x8-inch baking pan with parchment paper, leaving enough overhang on the sides to lift the bars out later.
02 - In a large saucepan, melt 1/2 cup unsalted butter over low heat. Add the sweetened condensed milk and granulated sugar, stirring constantly until the sugar fully dissolves.
03 - Remove the saucepan from heat. Stir in 1 cup semisweet chocolate chips, vanilla extract, and a pinch of salt. Continue stirring until the chocolate is completely melted and the mixture is smooth.
04 - Gently fold the cornflakes into the chocolate mixture, taking care not to crush them too much, until every flake is evenly coated.
05 - Transfer the cornflake mixture into the prepared baking pan. Press firmly and evenly into a uniform layer using a spatula or the back of a spoon.
06 - Combine 1 cup semisweet chocolate chips, 1/4 cup heavy cream, and 2 tablespoons unsalted butter in a microwave-safe bowl. Microwave in 20-second bursts, stirring between each interval, until the mixture is completely melted and silky smooth.
07 - Pour the fudge topping over the cornflake base, using a spatula to spread it into an even layer across the entire surface.
08 - Refrigerate the pan for at least 1 hour, or until the fudge topping is firm and set to the touch.
09 - Lift the slab out of the pan using the parchment overhang. Cut into 16 even bars and serve immediately, or store in the refrigerator until needed.