Cut the cucumber into thin slices, cut the onion into thin rings. Tear the dill.
Roughly crush the mustard seeds. Bring the water to the boil in a pan along with the vinegar, mustard seeds, sugar and salt, simmer for approx. 5 mins. Layer the cucumber, onion and dill in the clean, pre-warmed jars.
While still boiling hot, pour the liquid into the jars to just below the rim, seal immediately, leave to cool on a towel.
Cut the onion into thin rings, place in a small bowl, add the vinegar, sugar and salt, mix. Cover and leave to absorb for approx. 15 mins.
To boil the sausages
Cover and cook the sausages over a low heat in simmering water for approx. 15 mins.
Using the whisk on a mixer, beat the butter in a bowl for approx. 2 mins. until light and creamy. Finely chop the nuts, mix in along with the mustard. Cut the buns in half crosswise, spread the butter over the cut surfaces. Remove the lettuce leaves. Remove the sausages from the water, peel as desired, cut in half lengthwise, place on the bottom half of the bun along with several slices of pickled cucumber, onion rings and lettuce leaves, cover with the top half of the bun.