Line the baking tray with some parchment paper and lightly grease it all over with the oil
Mix the cornflour and icing sugar together and pass through a sieve. Dust the baking tray with some of it
Place as many oreo biscuits as you need to cover the bottom of the baking tin
Place and caster sugar and cold water into a deep saucepan and heat gently to dissolve the sugar
Add your thermometer and bring the syrup to the boil - DO NOT stir - and leave to 'cook' for approx 5 minutes until the temperature reaches to about 120oC
While this is doing, dissolve the gelatine in the hot water
Also whisk the egg whites until they hold stiff peaks
As soon as the syrup reaches the correct temperature, remove the thermometer and add the gelatine mixture (carefully) and leave to stand for a couple for minutes.
Then carefully pour the liquid into a heat resistant jug
Put the whisk on low and gradually add the hot syrup to the egg whites in a thin stream, whiskign the whole time. Then continue to whisk for about 5 more minutes until the mallow is glossy and thicker.
Then whisk in the vanilla extract
Pour the mixture over the oero biscuit base
Then crush thr remaining oreo cookies to make course crumbs and scatter these over the top off the mallow
Leave the mallow in a dry and cold place (I left mine inside my front porch) to set for 4-5 hours
Once set and ready, carefully ease the parchment paper from around it and cut into squares.
Using a deep tin meant mine were very big! But that is fine with me :)
Keep in an airtight container for up to 5 days
Recipe by Mummy Mishaps at http://www.mummymishaps.co.uk/2014/02/oreo-marshmallows.html