Put a saucepan of water on to boil for the egg vermicelli. Cut the chicken breasts diagonally into long, thin strips.
Peel the garlic and crush it into a bowl. Stir in the mustard, tomato paste, vinegar and stock or water.
Holding the spring onions together firmly, slice the green parts finely and push to one side, then slice the white parts finely and keep the two separate.
Heat 1½ tablespoons oil in a frying pan over high heat. Stir-fry the chicken for 1–2 minutes, until it turns white.
Stir the garlic and vinegar into the pan and add the white parts of the spring onions. Bring to the boil, cover and simmer gently for about 5 minutes.
Meanwhile, add the vermicelli and some salt to the pan of boiling water. Return to the boil and cook for 3 minutes, then drain well and toss in the remaining olive oil.
Blend the cornflour with a little cream and stir into the chicken. Add the green parts of the spring onions, reserving some for a garnish, then add the remaining cream and season to taste. Stir over moderate heat for 2–3 minutes, until the sauce thickens.
Serve the chicken and sauce over the vermicelli and garnish with the reserved slices of spring onion.
A fresh pasta such as spaghetti can be substituted for the vermicelli.
Have been looking for a recipe with a creamy tomato sauce and this fit the bill, next time I think I'd put maybe a tiny bit less wine vinegar cos that came through quite strong but otherwise I thought it was deluxe - 14 Feb 2010