In a small pot, add the vinegar, sugar, salt flakes, spices and bring to a gentle simmer. Simmer for a couple of minutes, the sugar and salt flakes must have dissolved and remove from the heat.
Slice the onion in rings and if you wish cut in half moon. Boil the kettle and place the sliced onion in a colander and pour over the hot water. Let the water drain and when it’s cooled down, transfer the onions in sterilised jars. Pour over the warm vinegar mix and seal.
You can leave the jars to chill. This red onion pickle can keep up to 6 months when unopened, once opened it keeps for 2 weeks in the fridge.