Place the peaches in a large, heavy-based saucepan with the orange juice and zest. Simmer for about 15 minutes until the fruit is soft.
Meanwhile, halve the vanilla pod lengthways then cut each half in 2, to give 4 pieces.
Add to the pan along with the jam sugar and continue to cook, stirring, until the sugar has completely dissolved, then boil for 10 minutes. Remove from the heat.
Check to see if the jam is ready to set: drop a teaspoonful of the jam onto a cold saucer, leave it for 30 seconds, then push your finger through it.
It should crinkle along the surface. If it doesn’t, return it to the boil for a minute or 2, and test again.
Skim the surface of the jam to remove any foam then leave it to stand for 10 minutes. Stir again then pour into warm, sterilised jars and seal. Once opened, store in the fridge for up to a month.