Rinse the 1 kg potatoes and place them whole in a large pot of cold salted water.

Bring the potatoes to a boil and simmer until completely tender when pierced, about 35 to 40 minutes.

Peel the warm cooked potatoes and pass them through the potato ricer onto a clean work surface.

Add the 340 g all-purpose flour and 1 egg to the riced potatoes.

Knead briefly just until a soft dough forms, taking care not to overwork it.

Divide the dough into portions and roll each portion into ropes about 2 cm thick.

Cut the ropes into small gnocchetti and roll each piece over the tines of a fork to create ridges.

Twist off the heads and peel the 15 langoustines, reserving the shells and heads for the sauce.

Chop the 3 celery stalks, 2 Tropea onions, and 2 garlic cloves into small pieces.

Heat 2 tablespoons of extra-virgin olive oil in a wide pan and sauté the chopped celery, onions, and garlic until softened.

Add the reserved langoustine shells and heads to the pan, then toast them for 3 to 4 minutes while pressing to release their flavor.

Pour in the 240 ml dry white wine and simmer until the wine has reduced by about half.

Add enough water to barely cover the shells and simmer the shell stock for 20 minutes.

Strain the shell stock through a fine-mesh strainer, pressing the solids to extract as much liquid as possible.

Return the strained shell stock to the pan and simmer until reduced to a concentrated sauce base.

Blend the reduced shell sauce until smooth, then return it to the pan.

Stir the 150 ml heavy cream and 40 g butter into the sauce, then simmer gently until glossy and creamy.

Season the langoustine cream with salt, black pepper, and the juice from half of the lemon.

Heat the remaining 1 tablespoon extra-virgin olive oil in a pan and sauté the peeled langoustine meat until just opaque, about 1 to 2 minutes.

Bring a large pot of salted water to a boil and add the prepared gnocchetti in batches.

Cook the gnocchetti until they float to the surface, then lift them out with a slotted spoon.

Toss the cooked gnocchetti with the warm langoustine cream until evenly coated.

Fold in the sautéed langoustine meat and finish with the remaining lemon juice and black pepper before serving.