1 small red onion, cut into 1/2-inch wedges
1 small sweet potato (about 8 ounces), cut into 1-inch pieces
1 carrot, peeled and cut into 3/4-inch pieces
1 parsnip, peeled and cut into 3/4-inch pieces
1 small celery root (about 12 ounces), peeled and cut into 3/4-inch pieces
1 small beet, peeled and cut into 3/4-inch pieces
3 tablespoons extra-virgin olive oil
Salt and freshly ground pepper
1/4 cup walnuts
1 1/2 teaspoons balsamic vinegar
1 1/2 teaspoons fresh lemon juice
1/2 teaspoon Dijon mustard
2 tablespoons chopped flat-leaf parsley
1 ounce feta, crumbled (1/4 cup)
Preheat the oven to 425. In a medium roasting pan, toss the onion, sweet potato, carrot, parsnip, celery root and beet with 2 tablespoons of the olive oil. Season the vegetables with salt and pepper and roast for about 45 minutes, stirring once or twice, until tender and lightly browned in spots.
Meanwhile, spread the walnuts in a pie plate and toast until golden, about 6 minutes. Transfer the walnuts to a work surface and coarsely chop.
In a large bowl, whisk the vinegar with the lemon juice, mustard and the remaining 1 tablespoon of olive oil and fold in the parsley. Season with salt and pepper. Add the vegetables and walnuts to the dressing and toss. Top the salad with the feta and serve warm or at room temperature.
The roasted winter vegetables and dressing can be refrigerated separately overnight. Rewarm the roasted vegetables before serving.