Preheat the oven to 200C/400F/Gas 6.
For the langoustines and oil, peel the langoustines and set the flesh to one side. Place all the langoustine shells, the tomato purée, the celery, carrot and onion into a bowl and mix together well. Place onto a baking sheet then place into the oven to roast for 30 minutes, or until golden.
Remove from the oven and reduce the oven temperature to 170C/325F/Gas 3.
Pour the oil over the roasted shells and vegetables and stir well. Return to the oven for a further hour then remove from the oven and drain off the oil by passing through a fine sieve into a bowl. Set aside the oil and discard the shells and vegetables.
For the tagliatelle, heat a frying pan until hot then add the olive oil, small courgettes and thyme. Fry until golden brown and just tender.
Meanwhile, bring a large saucepan of water to the boil then add a pinch of salt. Add the pasta and cook for two minutes.
Add the courgette ribbons to the water and cook for a further minute until just wilted. Drain the pasta and courgette ribbons and place back into the saucepan.
Add the sautéed courgettes and season with salt and freshly ground black pepper.
To serve, spoon out onto a serving plate. Place the langoustines on top of the pasta, sprinkle over the parmesan and spoon over a little of the langoustine oil. Serve immediately.