Recipe sourced from feed-your-sole.com
Serves 8 (2 Tbsp per serving)
1.1lb red onions, ends cut off and thinly sliced
1 Tbsp olive oil
1/3 cup white granulated sugar (caster sugar works well)
1/3 cup balsamic vinegar
1/4 cup red wine vinegar
2 cloves garlic, minced
1 Tbsp Dijon mustard
Heat the oil over medium heat and then add the onions. Cook for around 20 minutes, stirring often, until they are softened. If they start to brown at the edges, turn the heat down.
Add half the sugar and stir everything together well. Cook for another 10 minutes.
Add the remainder of the sugar, balsamic, red wine, garlic and mustard and stir to combine all well. It will look like there is a lot of liquid but it will reduce down.
Cook for a further 45 minutes until the liquid has reduced to a sticky consistency that is coating the onions. If you run a wooden spoon through the bottom of the pan, the juices should scrape away and there should be no liquid that pools in the gap you’ve made. Keep going if there is still too much liquid – if needed, increase the heat slowly to let more evaporate.
Cool the liquid and then spoon into sterilized jars. Seal and keep in the fridge for up to 3 months.
To sterilize the jar, wash in hot soapy water and then transfer into a warm oven (300°F). Leave in the oven for 20 minutes until fully dry and then cool before using.
The flavors of the marmalade will develop more over time so this is actually best made at least a few days or a week before you are planning on using it.
Make sure to use a good quality red wine vinegar. If it’s too ‘tart’ it can affect the flavor of the marmalade.