Peel the cucumber, cut in half lengthways and remove the inside. Then cut into slices.
Melt a good trick of butter in the saucepan, add the sugar and let it caramelize briefly. Add the cucumber, season with salt and pepper and deglaze with a good dash of balsamic vinegar. Stew for 5 to 7 minutes. Stir in mustard, crème fraîche and dill and serve.