If using pre-cooked peeled crayfish, check for any shells and pat dry with paper towels. If using whole cooked crayfish or langoustines, remove tails and discard shells. Keep tails chilled until assembly.

Dress the leaves

In a medium bowl, combine the watercress and optional baby gem lettuce. Add the extra-virgin olive oil, juice from half the lemon (reserve remaining half for serving), sea salt and freshly ground black pepper. Toss gently to coat the leaves evenly. Taste and adjust seasoning.

Prep avocado

Halve the avocado, remove the pit and scoop the flesh out. Slice or dice the avocado depending on desired presentation. Immediately toss the cut avocado with a teaspoon of lemon juice from the reserved lemon half to prevent browning and season lightly with a pinch of salt.

Marie Rose Sauce

In a small bowl, combine the mayonnaise and tomato ketchup until smooth. Stir in the lemon juice, Worcestershire sauce, optional hot sauce and optional grated horseradish. Season with salt and freshly ground black pepper. Taste and adjust acidity or sweetness by adding a little more lemon juice or ketchup. Chill the sauce for 10–15 minutes to let flavors meld.

Garnish & Assembly

Assemble the cocktail: divide the dressed watercress and leaves between 4 serving glasses or small bowls (this recipe makes 4 starter portions). Place a portion of avocado (about 1/4 of the avocado) over the greens in each glass.

Arrange 3 crayfish tails on top of the avocado in each glass, fanning them slightly for an attractive presentation. Spoon about 1 1/2 tablespoons of Marie Rose sauce over the crayfish and around the avocado (reserve a little sauce for serving if desired).

Garnish each cocktail with a sprinkle of snipped chives, a small sprig of dill and a very light dusting of sweet paprika. Add a lemon wedge to the rim of each glass for additional juice at the table.

Serve immediately while the greens are crisp and the crayfish are chilled. Offer extra cold Marie Rose sauce at the table.