Peel and dice the onion.
Heatthe butter and oil in a large pan over low heat and add the onions.
Coverthe pan and cook slowly for 1.5 hours, stirring occasionally.
Stir in the honey, salt, and pepper, and turn up the heat to medium. Mince the thyme and rosemary and stir into the pan.
Boil the mixture, stirring regularly until the liquid has been absorbed.
Take the onions off the heat and stir in the vinegar and minced tarragon.
Adjustthe seasoning with additional salt and pepper to taste.
Serve as it is or refrigerate for up to 3 weeks.If preserving, ensure you use sterilised jars that seal well.