Place all ingredients in a large saucepan.
Bring mixture to a simmer, stirring gently.
Let simmer for 10 minutes. DO NOT STIR during this cooking time. If there are sugar crystals on the side of the saucepan, use a heatproof brush dipped in a little milk to brush away.
Take off the heat and allow to cool for 15 minutes.
Beat using a wooden spoon until mixture loses its glossiness and becomes more creamy in texture. This should take less than 5 minutes. The moment between beating too little (and mixture being too runny) and beating too much (and mixture becoming stiff and sugary) is fast. Keep your eye on it and don't be tempted to overbeat once it's reached a creamy consistency which can still be poured.
Pour into a small, lightly buttered dish.
Mark into squares and cut once set.
Decorate with sprinkles.