Preheat oven to 180C. Spread your oats on a baking tray lined with parchment and toast for 10 minutes. Set aside to cool.
Beat the butter and sugars together on medium speed until light and fluffy, about 5-8 minutes.
Add the eggs and vanilla bean paste and beat for another 5 minutes.
In a separate bowl, mix together your dry ingredients: plain flour, salt, bicarbonate of soda and oats. Slowly add to the butter egg mixture in thirds, combining in between and scraping down the sides of your bowl to get everything mixed in nicely.
Add cornflakes and mix with a spoon until combined.
Refrigerate dough for at least 4 hours, although preferably overnight before baking.
When you’re ready to bake your cookies, bring the dough back to room temperature whilst you preheat the oven to 160C fan (I’ve lowered the temperature as this seemed to work better with my fan oven). Line your baking tray with parchment paper.
Measure out 50g balls of cookie dough and place about 3 inches apart on the baking tray.
Flatten slightly with your fingers (or the back of a spoon, dipped in flour to prevent sticking) and then grind or sprinkle some rock salt on each one.
Bake for 13-16 minutes, keeping an eye on them. They should be golden on the outside but stillappear slightly wet in the middle. This is important as it gives you the “chew”.
Once they’ve finished baking, let the cookies cool on your baking tray before transferring to a wire rack to cool completely.