Begin by making sure that you have all of your equipment ready and ingredients measured out, as you will need to work quickly once the honeycomb mixture is ready.
Line an 8 inch square pan with parchment paper and set aside.
Add the cornflakes to your food processor and blitz for a couple of minutes until they are ground down into a medium-fine crumb.
Add the sugar, golden syrup and water to a medium/large saucepan and place on a medium heat. Stir using a wooden spoon for a minute or so until all of the sugar has melted. At this point stop stirring the mixture, as continuing to do so will cause the sugar to crystallise.
Turn the heat up to medium-high and place your candy thermometer into the syrup to monitor the temperature. You want the syrup to get to 149°C (300°F), this will take around 15 minutes, so be patient but keep a very close eye on the pot.
Meanwhile add the peanut butter to a large heat resistant bowl and heat over a double boiler, whisking until smooth. Add the crushed cornflakes to the bowl and gently stir them together.
In a small bowl or glass, mix together the baking soda and vanilla extract.
Once the sugar syrup has reached 149°C (300°F), add the baking soda-vanilla mixture and whisk for a few seconds to combine the mixture. Be careful not to touch it as it will be extremely hot!
Pour the sugar syrup mixture into the peanut butter mixture and fold until combined, being careful not to over-mix.
Transfer the mixture to the lined pan and press it evenly into the edges, using a spatula or flat bottomed glass to even out the surface. Allow this to set at room temperature for 2 hours.
Once it is completely set and at room temperature, you can remove the butterfinger from the baking dish. Carefully cut it into bars using a sharp knife.
Melt the chocolate over a double boiler and coats the bars, using two forks to dip them into the chocolate. Sit the coated bars on a sheet of parchment paper and allow them to set completely for 1-2 hours.
Store in an airtight container at room temperature.