Homemade Butter

The chemistry behind butter-churning interests me, and I'd heard you could make butter from a tub of whipping cream, which is cheaper than butter. So this experiment was driven by both science and economics!

Ingredients:
300ml whipping cream
Pinch of salt

Method:
1) Tip the cream into a food processor, and turn on to medium for about 20 mins, or until it looks like butter
2) Separate the leftover liquid and keep or chuck
3) Wash the butter with water until the liquid runs clear
4) Add a pinch of salt, and use a wooden spoon to work it into the butter (not a metal spoon)
5) Keep in the fridge

Budget:
Cream = £1