Prepare two large baking sheets by lining them with parchment paper or silicone mats.

In a large saucepan, combine the light corn syrup and granulated sugar over medium heat.

Bring the mixture to a simmer, stirring constantly until the sugar is fully dissolved.

Remove the saucepan from the heat and immediately stir in the creamy peanut butter and vanilla extract until smooth.

Gently fold the cornflake cereal into the peanut butter mixture until all flakes are thoroughly coated.

Fold in the mini marshmallows quickly so they soften slightly without fully melting into the mixture.

Using a cookie scoop or two spoons, drop rounded tablespoons of the mixture onto the prepared baking sheets.

Allow the cookies to sit at room temperature for approximately 30 minutes until firm and fully set.