Before starting the recipe, note that these cookies must be stored in the freezer, or they lose their crunch and soften in the fridge.
Cover a large plate with parchment paper. Set aside.
In a large saucepan, combine the peanut butter, maple syrup, melted coconut oil, and vanilla extract. Cook over medium heat for 1 minute until all the ingredients are smooth and combined. Make sure to stir constantly, so it doesn't burn.
Remove from heat and stir in the cornflakes until the cereals are fully covered by the peanut butter mixture.
Use a tablespoon to drop the cookie batter onto the prepared plate, leaving half a thumb between each cookie as they can spread slightly.
Freeze the plate for about 10-12 minutes to set the cookies.
Store in a sealed container in the freezer for up to 3 months and eat straight out the freezer for a crunchy cookie. For chewy cookies, store them in the fridge. Don't store at room temperature or they will melt quickly under 73°F (23°C).