For the pasta, lightly crush the saffron in a bowl with the back tip of a wooden spoon, then soak in 1-2 tablespoons of boiling water. Leave to cool to room temperature. Place the rest of the ingredients into a food processor with a few drops of the saffron infused water and whiz until the mixture resembles coarse crumbs. Tip the mixture into a bowl and press together into a ball with your hands. Turn onto a lightly floured work surface and knead until the dough is smooth. It should be soft but not sticky. If it feels too wet, knead in a little more flour. Wrap in cling film and chill for 30 minutes before rolling out.
For the scallop mousse: Blend the scallops in a food processor with the double cream, lemon juice, lime zest and a little salt and pepper until smooth. For the crab filling, check the crabmeat for any pieces of shell then stir in the ginger, basil and lemon juice to taste. Check for seasoning. Add enough of the scallop mousse to bind the crab meat mixture lightly together.
With clean and very dry hands, shape the mixture into 12 small balls (no larger than a teaspoon). Chill while you deal with the pasta dough.
Crab and ginger tortellini
Lay the sheets of pasta on the work surface and cut out 24 rounds using a 5cm cutter. Press a ball of the crab filling onto one side of a pasta circle. Brush around the edges of the pasta with a little egg wash, then fold over the larger side to form a semi-circle. Starting from the top of the semi-circle, press the edges to seal, making sure that there are no air bubbles in and around the filling. Press the two ends of the semi-circle together by curling the tips of the edges around your index finger. Repeat with the rest of the filling and pastry rounds.
Blanch the tortellini in boiling salted water for 2 minutes then drain and immediately immerse in a bowl of ice-cold water. Drain again and lay out on an oiled tray in a single layer. Wrap in cling film and chill until ready to use.
For the vinaigrette, warm the olive oil with the shallots and ginger for about 10 minutes until the shallots and ginger have softened. Halve the tomatoes and stir through off the heat with some seasoning and balsamic vinegar to taste. Finely shred the basil and add to the dressing just before serving.
Bring a large pan of salted water to the boil, then cook the tortellini for 1-2 minutes until al dente. Remove them from the water with a slotted spoon and drain well. Drizzle with the vinaigrette and garnish with a sprig of chervil.