To make the souffles: Coat the bottom and sides of each of 8 buttered 1/2-cup ramekins with about 1 tablespoon of the walnuts and arrange the ramekins in a jelly-roll pan. Preheat the oven to 400 degrees F.
In a small saucepan melt the butter over moderately low heat, whisk in the flour, and cook the roux, whisking, for 3 minutes. Add the milk in a stream, whisking, and boil the mixture over moderate heat, whisking, for 2 minutes, or until it is thick and smooth. Transfer the mixture to a bowl and let it cool slightly.
Whisk in the yolks, 1 at a time, the goat cheese, the thyme, and salt and pepper, to taste, and whisk the mixture until it is combined well.
In another bowl beat the whites with a pinch of salt until they are frothy, add the cream of tartar, and beat the whites until they just hold stiff peaks. Whisk 1/3 of the whites into the cheese mixture and fold in the remaining whites gently but thoroughly. Divide the souffle mixture among the ramekins, sprinkle each souffle with about 1 1/2 teaspoons of the remaining walnuts, and bake the souffles in the upper third the oven for 20 minutes, or until they are puffed and golden.
Transfer a ramekin to each plate and serve the souffles immediately.
To make the salad while the souffles are baking: In a bowl, whisk together the vinegar, the mustard, and salt and pepper, to taste, add the oils in a stream, whisking, and whisk the dressing until it is emulsified.
In a bowl toss the watercress and the frisee with the dressing and divide the salad among 8 plates.