Peel the cucumbers, cut them in half lengthwise and remove the seeds. Cut the flesh into thick slices. Peel onions and cut into rings. Bring vinegar, 1 litre water, salt, sugar, mustard and peppercorns, bay leaf and onion rings to the boil.
Add cucumbers, bring to the boil and simmer for about 5 minutes. Meanwhile wash dill, shake dry and pluck roughly. Scoop the cucumbers out of the stock and fill into clean glasses with the dill. Pour the cucumber stock over them.
Immediately close tightly and allow to cool down. Store cucumbers in a cool, dark place. Shelf life at least 2 months.