For the crab ravioli mousse, place the scallops, egg yolk, cream and brown crab meat into a food processor and mix until smooth.
Remove the mixture from the food processor and spoon into a bowl suspended over ice.
Stir in the ginger and white crabmeat. Season with salt, freshly ground black pepper and a pinch of cayenne pepper. Add a few drops of lemon juice.
For the basil oil, heat the oil to 80C/175F (use a thermometer to check this) and add the basil. Infuse for a few minutes and then blend in a food processor until smooth. Pass the mixture through a fine sieve and set aside
For the basil purée, bring a pan of lightly salted water to the boil, add the basil leaves and cook for 1-2 minutes, or until soft and tender. Drain and refresh in iced water.
Pat the basil dry on kitchen paper, blend in a food processor until smooth and pass the mixture through a fine sieve.
For the ravioli pasta, place the basil purée, basil oil, egg, egg yolk, flour and salt into a food processor. Switch on the processor and slowly add the water until well combined. Remove the dough from the food processor, knead briefly until smooth, then wrap in clingfilm and chill in the fridge for 30 minutes.
For the sauce, heat a heavy-based saucepan until medium hot, add the butter, shallots, ginger and lemongrass and fry for five minutes.
Stir in the peppercorns and coriander seeds and fry for another two minutes.
Add the brown crabmeat and crab carcasses and fry for five minutes
Pour in the fish stock and bring to the boil then simmer for 20 minutes. Pass the mixture through a fine sieve into a clean saucepan.
To finish the sauce, add the butter, salt, freshly ground black pepper and lemon juice. Whisk until well combined.
Split the crab mousse into four equal portions.
Roll the pasta out thinly using a pasta machine or rolling pin. Using a pastry cutter, cut the dough into 10cm/4in circles.
Place a spoonful of crab mixture onto a pasta circle, fold the top over to form a semi-circle, press down lightly to seal then wrap the edges of the semi-cirlce around your index finger and join together.
Bring a saucepan of salted water to the boil, add the pasta and simmer for 4-5 minutes. Drain.
To serve, place the tortellini into serving bowls, pour over the sauce and scatter with pink grapefruit and cress. Drizzle with a little basil oil.