Steamed leeks and sautéed mushrooms make a robust salad that's especially welcome in the autumn and winter months. The earthy richness of the mushrooms balances the mild onion flavor of the leeks perfectly. Any variety or combination of mushrooms will do nicely. Add a vinaigrette made with walnut oil to enliven the salad, plus a handful of toasted pine nuts for a contrast of texture, and you have a dish to treasure.
Combine the walnut oil, vinegar, mustard, lemon zest, salt, pepper and parsley in a glass jar. Cover tightly and shake vigorously to combine. Set aside at room temperature.
Cut each of the leeks on the diagonal into three pieces. Steam the leeks until they are tender. Transfer the leeks to a shallow pan and drizzle with two-thirds of the dressing. Let the leeks cool in the vinaigrette at room temperature.
Place the olive oil in a very large skillet and heat over medium-high heat. When hot, add the mushrooms and cook without stirring until they turn crisp and golden, about 4 minutes. Then stir and continue cooking until they're tender and browned. Transfer to a platter and let cool.
To assemble the salad, place the greens in a large bowl and toss with some of the remaining vinaigrette. Divide the greens among 4 plates and arrange the leeks atop each serving. Scatter the mushrooms over the leeks and sprinkle with the pine nuts. Serve immediately.