Add the unsalted butter, peanut butter, light brown soft sugar and white granulated sugar to a bowl and beat until creamy - I use my stand mixer with the beater attachment!
Add in the egg and vanilla extract and beat again.
Add in the plain flour, cornflour, baking powder, bicarbonate of soda, and salt and beat until a cookie dough is formed. (If the mixture is too dry, add 1-2tbsp of milk - dryness can come from certain brands of peanut butter!)
Add in the white chocolate chips, peanut butter chips and peanuts and beat until they are distributed well.
Weigh the cookies out into eight cookie dough balls - they're about 125g each!
Once they are rolled into balls, put the cookie dough in the freezer for at least 30 minutes, or in the fridge for an hour or so!
Whilst the cookie dough is chilling, preheat the oven to 180ºC Fan, or 200ºC regular! If your oven runs hot, go for 160ºC-170ºC.
Take the cookies out of the freezer/fridge and put onto a lined baking tray. I put four cookies per tray!
Bake the cookies in the oven for 11-12 minutes. I don't personally flatten the cookies, as they flatten enough during baking - however, if you like flat cookies, flatten them a bit before baking.
Once baked, leave them to cool on the tray for at least 30 minutes, as they will continue to bake whilst cooling!
ENJOY!
Notes
These are best eaten on the day of baking, but can be revived by microwaving for 15-30 seconds, or putting into a hot oven for 2-3 minutes!
I used smooth peanut butter for these.
I found my Reeses peanut butter chips in Sainsburys!
If you prefer your cookies flatter, you can squish them down slightly before baking but I don't do this personally!
If you don't want to use cornflour you can remove it and use 25g more flour instead.
If you can't access one of the sugars, use all of the other one - i.e. all granulated, or all light brown sugar. Using other sugars can change the texture.
If you want to make smaller cookies (60g) - they take about 9 minutes to bake!