Peel, wash and slice the potatoes. Cook in the boiling broth for about 10 minutes. Pour off, collect the stock and measure 200 ml of it. Whisk 100 g flour, egg and beer.
Season with salt and pepper. Pass the dough through a sieve and let it swell. Wash the fish, dab dry and cut into large pieces. Sprinkle with lemon juice. Heat the frying fat in a large pot or deep fryer.
Dice the bacon. Heat the fat in a pan and fry the bacon in it until crispy. Sprinkle with the rest of the flour and sauté briefly. Add measured stock and milk while stirring and let simmer for about 5 minutes.
Season to taste with salt and pepper. Dice cucumbers. Wash the dill and chop finely, except for a little bit for garnishing. Add potatoes, cucumber and dill to the bûchamel sauce. Pull the fish through the beer batter and bake in hot frying fat in portions for about 5 minutes until golden brown.
Drain on kitchen paper. Arrange on a plate with the béchamel potatoes. Garnish with dill and lemon.