Toast the oats in a dry frying pan over medium heat, stirring so it doesn't burn. Remove from the heat and set aside to cool.
Beat the whipping cream till stiff. Add the oats a handful at a time till desired consistency is reached. There shouldn't be too many oats - make sure it's still light and creamy.
Add caster sugar to taste, along with rum or vanilla.
Add some fresh berries and gently fold into the cream mixture. Serve straightaway.