Mix together the juice of one lemon, 2 tbs olive oil, 1tbsp mayonnaise till well-blended. Season with sea salt and pepper. 

Slice up a peeled shallot into rings. Place in a small bowl of water along with a large pinch of coarse salt (this will remove the bitterness of the onion). 

Slice up a dozen radishes (use multi-coloured ones if you can find these).

Peel 300g cooked potatoes and cut into chunks. While still warm, pour over the sauce and mix.

Mix in the radishes, the drained shallot, and a sprinkling of fresh dill (chopped).