Mix the minced meat with the mustard, salt and pepper, the egg and the breadcrumbs. Mix until the mixture is firm and smooth, then add sparkling water until the mince is just slightly looser and easier to stir. Leave the mince to rest in the fridge whilst you prepare the rest.
Shape the mince into 4 large, flat patties. Set out three plates: one with flour, a deep plate with the eggs beaten with a little water, and a plate with breadcrumbs, well seasoned with salt and pepper.
Using your left hand, first coat the cutlet in flour, then in the egg, before using your right hand to lift it out of the egg and into the breadcrumbs. This ensures the smoothest finish, without any breadcrumbs in the flour or egg in the breadcrumbs.
Fry the cutlets in butter for about 5 minutes on each side over a medium heat. Leave them to keep warm in the pan until serving.
Boil the small potatoes in plenty of salted water until just tender, then keep them warm.
Blend the parsley leaves with the olive oil, garlic and ½ tsp salt.
Place a pan of salted water on the hob. Meanwhile, trim the tops and bottoms off the carrots and scrub them thoroughly. Cut the carrots on the diagonal and place them in a small bowl. Rinse and slice the spring onions diagonally into bite-sized pieces.
When the water is boiling, cook the carrots for 2 minutes. Add the sliced spring onions to the boiling water, cook for a minute, then immediately transfer them to a bowl of ice-cold water. Leave them to cool for 3 minutes, then drain them in a sieve.
Finely chop the chives and finely chop the shallot. Rinse and cut the radishes in half or into quarters if they are large. Pick and roughly chop the dill.
Cut the potatoes, whilst still warm, into halves or quarters, depending on their size.
Take a good-sized, wide saucepan or frying pan and heat it over a medium heat. Add a third of the parsley oil, then add the potatoes, carrots and spring onions. Stir and heat everything through for about 2 minutes, but without letting it get too hot – the salad should only be warm.
Finally, add the radishes and toss everything together. Remove the saucepan from the heat and stir in the remaining parsley oil, along with the lemon juice, dill and chives. Gently toss the salad, season with salt and pepper, and serve it on the plates alongside the meatballs.
