The cream in whipped cream is what gives it that expandable, fluffy, thick quality we all know and love. This is thanks to the high fat content of cream--sinful yet delicious. Physically churning the cream creates air bubbles that fat molecules cling to, allowing it to maintain its fluffy state. The proteins and lactose combine and collect inside the air and fat molecules, making the cream stiffen. After some time, the air bubbles start to burst and the whipped cream breaks down, returning the cream to its original runny consistency. If this happens, all it takes it a quick fix to re-thicken the cream.
Pour the cream into a chilled mixing bowl. It's important you keep the cream as cool as possible.
Gently stir the cream using a cold spoon. This will combine the elements of the cream, as some separation may have occurred since you last whipped it.
Add a couple of tablespoons of fresh cream to the bowl and stir gently. Although this is not essential, it does help in the process.
Set the electric whisk to a slow speed. Turn it on and start to whisk the cream. Initially it will be runny. Increase the speed to medium and whisk until you see the cream starting to thicken. Gradually pour in 2 tbsp. of caster sugar while continuing to mix. You can use regular granulated sugar if you don't have caster sugar.
Turn the whisk to high and let it churn the cream until it completely re-thickens. It will form small but firm peaks when it's done. Turn off the whisk and return the re-whipped cream to the fridge until ready for use.