Make the honey-mustard dressing: pour all the ingredients into a big jar, close the lid, and shake with the jar intensively until the sauce is smooth.
Prepare all the ingredients: Peel the potatoes and cut into 1.5-inch (4cm) chunks. Cut both ends of the radishes and cut them into 2 or 3 parts. Shred the fish into small chunks (check if there are no grates!), finely chop the dill. Cut off the woody ends of asparagus (where it changes color from green to white) and cut into 2 or 3 parts.
Cook the potatoes, asparagus, and eggs: I like to cook these three ingredients together to save up on washing dishes. Potatoes cut into chunks need about 12 minutes cooking time over medium heat, hard-boiled eggs need 8 minutes, asparagus needs 3-8 minutes (thin asparagus like on the photos needs 2-3 minutes, very thick about 8 minutes). How to cook it: add the potatoes into a large pot, season with salt, pour boiling water over. Bring to a boil, cook for 4 minutes, add the eggs, cook for 5 minutes, then add the asparagus and cook for 3 minutes. Drain. Add the eggs into very cold water and the potatoes and asparagus back to the pot. Peel the eggs and cut into quarters, add to the pot.
Cook the radishes: Heat the butter in a medium pan, add the radishes. Cook for about 5 minutes, stirring from time to time, until soft and lightly browned. Add the radishes to the other ingredients in the pot.
Assemble: Toss all the ingredients with the dressing and chopped dill until combined. Do this immediately, potatoes need to be hot so that they can soak up the dressing. Season again with salt and pepper.