Peel the pumpkin, remove the seeds, cut into small slices with a colored knife and place in a bowl. Mix 1/8 litre vinegar and 1/8 litre water and pour over. Place in a cool place and let it stand, preferably overnight.
Wash the lemon, peel thinly, cut in half and squeeze the juice. Cut the vanilla pod lengthwise, scrape out the pulp, quarter the pod. Peel the ginger. Boil up sugar, remaining vinegar, 3/8 litres of water, lemon juice and zest, ginger, vanilla pod and pulp, cinnamon sticks and cloves.
In the meantime drain the pumpkin. Wash and dry preserving jars thoroughly. Boil rubber rings in water for a few minutes. Leave rings in cold water until used. Add pumpkin slices in portions to the sugar-vinegar stock.
Bring them to the boil briefly until they are glassy. Take them out immediately with a skimmer and fill them into the glasses. Let the vinegar-sugar stock cool down and pour over the pumpkin. Place the rubber ring and lid wet on the cleaned glass rim.
Close the glasses with hangers or clips and place them in the fat pan filled with hot water to boil down. Cook in the preheated oven (electric cooker: 200 °C/ gas: level 3). The glasses must not touch each other.
Switch off the oven as soon as it starts to bubble in the glasses (after about 60 minutes). Leave it in the oven for about 30 minutes. Do not open the oven door during the boiling time.