Toast the pecans in a medium skillet over medium heat, stirring, about 5 minutes. Transfer to a cutting board; let cool, then coarsely chop.
Line 2 baking sheets with parchment paper. Toss the pecans and cornflakes in a large bowl.
Make the caramel: Bring the butter, cane syrup, heavy cream and salt to a boil in a medium saucepan over medium heat and cook, stirring with a wooden spoon, until the mixture pulls away from the sides of the pan and comes together into a loose ball, about 5 minutes. Remove from the heat. Once the caramel stops bubbling, stir in the semisweet chocolate until melted.
Pour the chocolate caramel over the cornflake mixture and toss to coat. Scoop heaping tablespoonfuls of the mixture onto the prepared baking sheets and pack into compact mounds with your fingers. Let set, about 1 hour.
Put the white chocolate in a small microwave-safe bowl and microwave in 30-second intervals, stirring, until melted. Drizzle over the cookies and let set, about 1 more hour.