How to Make It
In a bowl, whisk the vinegars with the shallot and sugar; whisk in the remaining ingredients.
Preheat the oven to 350°. Brush the baguette slices with the olive oil and arrange on a baking sheet. Bake the croutons for about 10 minutes, or until lightly toasted.
In a pie pan, toast the hazelnuts in the oven until browned, about 10 minutes. Transfer the nuts to a kitchen towel and rub well to remove the skins. Coarsely chop the nuts.
In a saucepan of boiling salted water, cook the haricots verts until just tender, about 3 minutes. Drain, then rinse under cold running water until cool; pat dry.
In a large skillet, melt the butter over moderately high heat. Add the chanterelles and reduce the heat to moderately low. Cook slowly, allowing any exuded juices to evaporate, about 4 minutes. Increase the heat to high, season the mushrooms with salt and pepper and cook until lightly browned, about 3 minutes. Add the shallots, garlic, parsley and thyme leaves and cook, stirring, until fragrant, about 1 minute.
Spread the croutons with the Vacherin. In a large bowl, toss the arugula and haricots verts with the vinaigrette. Mound the salad on plates. Spoon the mushrooms on top and garnish with the hazelnuts. Set a crouton beside each salad, sprinkle pepper over all and serve.