Slice the potato very thin using a mandoline or other hand-held slicer. Brush a baking sheet with oil and arrange the slices in a circle, overlapping them slightly on the sheet. Brush the potato rings lightly with the oil and bake them in a preheated 375 F oven for 10 to 15 minutes or until they are golden. Transfer them carefully to paper towels to drain and sprinkle with salt to taste.
In a bowl whisk together the vinegar, mustard and salt and pepper to taste. Slowly whisk in the oil and then add the herbs and garlic.
Arrange the mushrooms in one layer in a jelly roll pan and sprinkle half the dressing over them. Let them marinate for 30 minutes at room temperature. Roast the mushrooms in the preheated oven for 10 to 15 minutes or until tender. Slice thin on the bias.
Toss the mesclun with the remaining dressing and mound one fourth of the salad on each of 4 plates. Fan out the mushroom slices on top of the salad and top each plate with a potato ring.
Recipe courtesy of Gourmet Magazine