Step 1

Cook the potatoesPeel or scrub the potatoes, cutting any large ones in half.Put in a saucepan with enough cold water to cover plus 2 tsp of salt.Bring to the boil then turn down to a simmer.Cook until the potatoes are just tender (15-20 min) then drain in a colander and set aside.

Step 2

Boil the eggs (do this while the potatoes are cooking)Put the eggs in a small saucepan and cover with cold water.Bring to a boil then turn down to a simmer.Cook the eggs for 8 minutes then drain and quickly cool under running water.Cover with cold water until completely cold, then shell and cut into quarters or eighths.

Step 3

Make the dressingIn a bowl or jug, stir together the mayonnaise, yogurt and horseradish sauce.Stir in the chopped gherkins and garlic plus some black pepper.

Step 4

Mix the saladCut the cooked potatoes into bite-sized pieces and put in a serving bowl.Add the red onion to the bowl along with most of the herbs (same some for a garnish if liked).Pour over the dressing and mix everything together well.Add the chopped eggs and flaked mackerel to the bowl and carefully fold them through the potatoes, trying not to break them up too much.Taste and add some salt if needed and/or more black pepper.Chill for at least 30 minutes before serving with any reserved herbs scattered over the top.

Step 5

Can be made up to a day in advance. Eat within 2 days.