Put prawns, dill, lemon zest and black pepper in a bowl and mix well. Place in a kilner jar, cut rounds of baking parchment to fit the top and cover prawns, compress down with a weight on top.
Melt butter and clarify by spooning off the clear liquid on top and discarding the cloudy part at the bottom.
Remove weight and paper from the prawns and spoon the clarified butter over them. Put baking parchment back on top and again compress with a weight. Let it set in the fridge for at least 1 hour.
Cut the tomatoes in half and, using a mandolin, slice the cucumber into thin ribbons and mix together. Serve the potted shrimps with bread and the salad.