To make the pasta dough, bring all the ingredients together in a food processor and rest for one hour.
To make the filling, sprinkle the apple and cucumber with salt and set aside for half an hour, then squeeze out the excess liquid.
In a large mixing bowl mix the crab, lemon zest, chives, apple and cucumber. Season to taste and set aside in the fridge.
For the dressing, heat the apple juice in a pan to reduce it in volume down to a light syrup. Whisk in the rapeseed oil and the toasted nigella seeds and lemon juice.
Roll the pasta through the pasta machine until it is smooth and perfectly thin.
Cut the sheet of pasta into 40 x 15cm/6in squares. This should give you enough space to fill and cut the ravioli out.
With a tablespoon make a small pile of the crab filling in the middle of 20 of the squares.
Brush around the filling with water and put another pasta square on top to form a lid. Working from one side of the square seal each parcel all around ensuring that all the air has been removed (otherwise they will burst when cooked). Use a8½cm/3½in wide round pastry cutter to measure out each ravioli, and cut around the pastry cutter with a knife. Check the edges are sealed again. You should be able to make 20 ravioli. Place them on a sheet of floured cling film laid on a baking tray. Set them aside in the fridge until ready to cook.
Heat a dry frying pan and brush the spring onions in a little oil and season with salt. Add to the pan to colour and steam for a few minutes until slightly charred.
To cook the ravioli, heat a pan of salted water to boiling. Add the ravioli and boil for a couple of minutes until cooked to your liking and heated through. Once cooked, remove from the water, drizzle with olive oil and season with sea salt.
To serve, put the ravioli in the bottom of a pasta bowl and lay the charred spring onions over and dress with the apple and nigella seed dressing.