Nigel Slater’s open sandwich recipe

In the open: Nigel Slater’s open sandwich recipe. Photograph: Jonathan Lovekin for the Observer

The recipe

Cut a ciabatta loaf in half horizontally. Toast the bread on the cut side. Put four heaped tablespoons of good mayonnaise in a mixing bowl, season it with black pepper and with the finely grated zest of a small lemon. Reserve the lemon. Finely slice four large radishes and put them in a mixing bowl. Trim three spring onions, discarding the tough, darker stalks, then cut the rest into small pieces and add to the radishes. Drain 100g of crayfish tails or prawns and roughly chop them. Wash a handful of watercress, discard any tough stalks, then add to the radishes together with a trickle of olive oil and a little sea salt and toss the mixture gently. Cut each half of the ciabatta into two. Spread the lemon mayonnaise over it, then divide the crayfish salad between them. Serves 2.

The trick

There is no second slice of bread under which to hide your filling. An open sandwich needs to be made at the last minute if it is to tempt. Keep the flavours light and fresh, and pick out only the most perfect of young salad leaves and herbs.

The twist

What you need on the toasted bread is a mixture of fresh seasonal salad and shellfish, and something to hold them in place. Use a classic mayonnaise or one seasoned with crushed, roasted garlic; or maybe a herb mayonnaise scented with tarragon or basil. Keep some crunch in the salad with radishes and spring onions, but also include cubed cucumber, coarsely grated celeriac or kohlrabi. Use cooked mussels from their shells, boiled brown shrimps or crab in place of the prawns.