Cut the rhubarb in small pieces and transfer them into a pan. Also add the sugar. Then cover the pan with a lid and heat it up on low heat till the rhubarb falls apart. This takes around 15 to 20 minutes.
Once that’s done pour the compote on a sieve that’s lined with a kitchen paper to clarify the broth. Let it drain in your fridge for a couple of hours.
Then pour 200 grams of the rhubarb broth into a saucepan and also add the Pedro Ximénez sherry, the white balsamic vinegar, the agar powder and the tarragon. Mix this well and then bring it to a boil for at least 30 seconds.
After that pass it through a fine sieve and let it cool down completely in your fridge. Then transfer it into a blender and blend it till smooth.
Now I always vacuum my gels. By doing this you will remove the air bubbles and that will leave you with a lovely clear and intense gel.
You can keep the gel for 3 days in your fridge and if you want to freeze it for a couple of weeks. If frozen be sure to let it defrost in your fridge. This way the gel will keep it's thick texture.