Preheat the oven to 400°F (200°C) and prepare a baking sheet lined with aluminum foil.

Wrap beets in aluminum foil, add a splash of water, and roast for 50–70 minutes until tender.

Chop carrots and shallots, coat with olive oil, salt, and pepper, then roast for 30–40 minutes until caramelized.

Blend champagne vinegar, Dijon mustard, salt, onion powder, and tarragon, then gradually add olive oil until smooth.

Let roasted beets cool, then slice and dice along with carrots and shallots.

Toss roasted vegetables with half of the vinaigrette and marinate for at least 10 minutes.

Fold in baby spinach and remaining vinaigrette before serving, then top with pistachios and feta.