Homemade dulce de leche (caramelised milk spread)

1. Pour the milk into a large, heavy-based pan, add the sugar and the vanilla pod split lengthways and bring to the boil over a medium heat, stirring, until the sugar dissolves.

2. When it boils, take the pan off the heat and stir in the bicarbonate of soda – the milk will foam up, so use a big pan; the bicarbonate helps develop a lovely brown colour and stops the milk curdling.

3. Return to the heat and simmer gently, uncovered, for 2½-3 hours, stirring every 10-15 minutes.

4. For the last 30-40 minutes, when it's thickening and caramel-coloured, stir constantly so it doesn't catch; remove the vanilla pod.

5. It's ready when a drop on a cold plate doesn't spread and a wooden spoon leaves a trail in it – it thickens further as it cools.

6. Pour into clean, hot jars and leave to cool; it keeps 3-4 weeks in the fridge.

Tip: Argentinians and Uruguayans still argue over who owns dulce de leche – it goes on bread, pancakes (panqueques), in alfajores and ice cream, and it even has a national day: 11 October.