3 litres milk
¾ teaspoon bicarbonate of soda
1 vanilla pod
Place milk and sugar in a large saucepan and cook over a medium heat, stirring constantly with a wooden spoon, until sugar is completely dissolved.
Bring to the boil and stir in vanilla pod and bicarbonate, dissolved in some cold milk. Lower the heat and keep cooking, stirring from time to time at the beginning and constantly when mixture begins to thicken.
Test the stage of this sweet removing some of it with a spoon and pouring it onto a dish. Cool. It must be firm not flow over the dish when swirling it.
Remove from heat.
Pour into a bowl, over a large saucepan with cold water, stirring continuously until it cools completely.
Store in glass jars inside the fridge.