Prep your space first. Line a baking sheet with parchment or a silicone mat. Lightly grease a spatula to make spreading easier. Set the cornflakes in a large mixing bowl.

Warm the peanut butter in a medium bowl in the microwave for 20 to 30 seconds until loosened.

In a medium pot, add the sugar, corn syrup, butter, and salt. Warm over medium heat, stirring until the sugar dissolves. Simmer gently for 1 minute when it starts bubbling.

Take off the heat and stir in the vanilla, then whisk in the warmed peanut butter until completely smooth.

Pour the hot mixture over the cornflakes. Use a wide spatula to fold the cereal until coated.

Scrape the mixture onto the prepared baking sheet and spread into a thin, even layer about a quarter inch thick.

If desired, sprinkle with flaky sea salt or sprinkles. Let it cool at room temperature for 30 minutes to 1 hour until firm.

Break into pieces with your hands or a butter knife.