Cut the pickling cucumbers in half lengthways, and slice regular ones through the middle, then into fingers. Peel and finely slice the shallots. Put the cucumbers and shallots in a colander. Sprinkle over 2 teaspoons of sea salt. After 45 minutes, rinse well. Combine all the other ingredients in a pan and bring to the boil. Stir until the sugar dissolves. Fit the cucumbers snugly into a Kilner jar, then pour over the liquid. Seal and leave for at least 24 hours.