Wash the jar you want to use in hot soapy water. Rinse it thoroughly and leave to dry. Important note: make sure you use a container made from either glass or ceramic. Metal and plastic can react with vinegar, ruining both your pickles and your container.
Clean the fennel and separate the leaves. Cut both the fennel and garlic into thin slices.
Add the vegetables and spices to the jar.
In a pan combine the vinegar, sugar, salt and turmeric. Bring the mixture to the boil, making sure everything has dissolved.
Once the vinegar is hot, pour it into the jar immediately. Add enough vinegar to cover all of the fennel, then put on the lid. Let the jar cool before storing it in the refrigerator.
You can eat your pickled onions immediately but it’s better to let the flavors develop for at least 24 hours.