For the brook trout a la tyrolienne, salt the cleaned trout well on the outside and inside, first pull through the milk and then turn in flour. Heat enough fat in one (or more) suitable frying pan and fry the char swimming in it until golden on both sides.
Meanwhile, prepare the mayonnaise sauce by mixing the egg yolks with a little mustard, a dash of lemon juice, salt and pepper until smooth. Slowly pour in the oil drop by drop, stirring constantly, until the mayonnaise is nicely thickened. Season the mayonnaise with a pinch of sugar, anchovy paste, tomato paste and grated horseradish.
Lift the char out of the fat, dab well with kitchen paper, arrange with lemon slices and serve the brook char a la tyrolienne with the prepared sauce.