Trim the beetroot stems to 1" and wash them well.
Place in a large saucepan and cover with water. Bring to the boil.
Reduce to a simmer and put a lid on. Simmer for 1 hour.
Meanwhile, sterilise your jar (see below).
Pour the vinegar in a small saucepan and bring to the boil. Add the sugar to taste and keep hot (but not boiling) until your beetroot is ready.
When the beetroot is cooked, drain the water and peel the skins off.
Thinly slice it with a sharp knife then fill your hot jar to the top with beetroot.
Pour over the hot vinegar (as close to the top as you can) and seal.
Preheat your oven to 190°C/Fan 180°C/374°F and make sure your jar is clean. (Washed in hot soapy water.) Place your jar on a baking tray, with seals removed, and bake for 20 minutes.
Seal while your jar is still hot for best results.
