Add the beans to a saucepan of boiling water and cook for 3 minutes, until just tender. Drain and refresh under cold running water. Halve the beans and put into a large salad bowl. Add the lettuce, witlof, celery and chicken. Cover and refrigerate until serving time.
Tip the anchovies into a bowl with the oil from the can (about 1 tablespoon). Add the garlic and use a fork to mash it to a paste. Thinly spread the paste over one side of each slice of baguette. Arrange on a baking tray and bake for about 10 minutes, until the croutons are crisp and golden. Cool slightly, then break into pieces.
While the croutons are cooking, make the dressing. Put the egg in a saucepan, cover with cold water and bring to a boil. Reduce the heat and simmer for 10 minutes. Drain the egg and cool under cold running water, then peel and chop. Whisk the oil, yogurt, vinegar, mustard, worcestershire sauce and sugar in a bowl. Season with freshly ground black pepper, then stir in the egg.
Drizzle half of the dressing over the salad and toss until the ingredients are evenly coated. Add the croutons and toss again. Drizzle with the remaining dressing and then scatter with the parmesan shavings. Serve at once.
Per serving: 497 calories, 42 g protein, 28 g fat (7 g saturated fat), 19 g carbohydrate (6 g sugars), 6 g fibre, 1147 mg sodium