Pulse the flour, egg, egg yolks and semolina in a food processor until well combined and the mixture comes together as a dough. Put the dough in a bowl, cover with cling film and rest in the fridge for 30 minutes.
Cut the pasta dough in half. Feed the pieces one at a time through a pasta machine according to the machine instructions, ending on the thinnest setting.
Mix both crab meats in a bowl with a little lemon juice. Season to taste with salt and pepper.
Lay a sheet of pasta onto a floured work surface and stamp out discs 6-8cm/2½-3in wide. Put a spoonful of the crab mixture onto each disc and brush the edges of the pasta lightly with the beaten egg.
Fold one half of the pasta over the filling then press lightly to seal. Pick the crescent of pasta up and twist the edges together, forming a little lip on the outside edge of the pasta. Repeat with the remaining pasta and filling then set the tortellini aside, covered in cling film, until ready to cook.
For the lemongrass and ginger sauce, clean the shellfish and remove and beards from the mussels. Discard any that are cracked, and any open shells that do not close when given a sharp tap.
Heat a large saucepan with a lid and add the mussels, clams, wine and coriander stalks. Cook with the lid on for 2-3 minutes or until all the shells are open. Discard any that do not open.
Strain, keeping the liquor, and remove half the mussels and clams from the shells and keep the other half in their shells for presentation.
Heat a sauté pan until hot and add the butter, shallots, ginger and lemongrass and fry for 5 minutes.
Pour in the liquor from the mussels and clams, add the fish stock and bring to the boil, then simmer for 3-4 minutes. Pass the mixture through a fine sieve into a clean saucepan.
To finish the sauce, add the cream, salt, pepper and lemon juice. Whisk until well combined.
For the spinach, heat a large sauté pan and add the butter and cook the spinach for 1-2 minutes or until wilted.
To cook the pasta, heat a large saucepan of salted water. Once boiling add the tortellini and cook for 1-2 minutes or until they float to the top.
Place the wilted spinach in the centre of the serving bowl and top with the tortellini. Spoon the sauce over the top and garnish with mussels, clams and coriander cress.