4 pounds sweet potato, peeled and cut into 1/2-inch dice
6 tablespoons vegetable, canola, or grapeseed oil, divided
Kosher salt
4 medium carrots, peeled and diced
1 medium onion, chopped
5 cloves garlic, crushed
2 sprigs sage (optional)
2 quarts homemade or store-bought low-sodium chicken stock or vegetable stock
1/4 cup fresh juice and 1 tablespoon freshly grated zest from 1 medium orange, divided
3/4 cup shelled roasted pistachios, crushed in a mortar and pestle or food processor
2 scallions, thinly sliced, white and light green parts only
2 tablespoons very thinly sliced fresh mint leaves (from about 5 sprigs)
Pinch cayenne pepper
1/2 cup extra-virgin olive oil