Peel and quarter the pears and apples, remove the core and dice or grate them very small. Mix with the squeezed lemon juice and the preserving sugar and let the juice steep overnight.
The next day, wash and dry the tarragon (French) and finely chop the leaves. Add to the fruit mixture.
Bring everything to a boil over high heat while stirring, then cook over medium heat for 4 minutes.
Make a gel test. Pour the jam into jars rinsed with hot water and close immediately.