Wash the cucumber and slice. Mix vinegar, mustard, salt and pepper. Fold in olive oil. Peel onions. Cut 1 onion into slices and chop the other finely. Wash the dill, dab dry and pick the tips off.
Add cucumber, diced onion and dill to the vinaigrette. Wash the plaice thoroughly and dab dry. Sprinkle with lemon juice. Cut the bacon into cubes. Heat a large coated pan, leave the bacon crisp in it and remove.
Dab the plaice dry and season with salt and pepper. Put the flour on a large plate and turn the plaice in it. Tap off excess flour. Add 1 teaspoon of clarified butter to the bacon fat in the hot pan and fry the plaice one after the other for 4-5 minutes on each side.
Keep warm. In the meantime peel, wash and slice the potatoes. Heat oil in a coated pan. Fry the potatoes for about 20 minutes until golden brown. After 10 minutes frying time add onion slices to the potatoes.
Season with salt and pepper and keep warm. Clean fish pan and heat bacon with 1 teaspoon of clarified butter again briefly. Arrange the fried potatoes, cucumber salad and plaice on plates. Spread hot bacon over the plaice.
Serve garnished with lemon and dill.