Method

• Slice the cucumbers and onions very thinly (a mandolin is ideal for this)
• Layer them in a bowl, sprinkling with the sea salt as you go, then weigh them down with a plate and leave for a few hours or overnight
• Drain off the liquid, rinse the vegetables well and drain in a colander
• Combine the vinegar, sugar, mustard seeds, and peppercorns in a pan and bring slowly to the boil, stirring to dissolve the sugar
• Add the well-drained cucumber and onion mixture and bring back to the boil for 1 minute, add the dill
• Bring the liquid back to the boil and simmer until slightly reduced for about 15 minutes, then divide it between the jars, filling to the brim
• Put on the lids and label
• The pickle will keep for several months