1  head cauliflower (about 1 1/2 pounds), broken into florets, and florets halved
1 3/4 teaspoons kosher salt
1 tablespoon pure olive oil
1  medium yellow onion, finely diced
1 tablespoon curry powder
1 tablespoon sugar
1 cup plain whole-milk yogurt
1/4 cup sour cream
1/3 cup packed, coarsely chopped flat-leaf parsley
dash freshly ground nutmeg
dash cayenne pepper
 freshly ground black pepper

Fill a 4-quart saucepan with 2 inches of water and bring to a boil over high heat. Add the cauliflower and 1/4 teaspoon of the salt. Partially cover the pan, adjust the heat so the water simmers, and cook the cauliflower until tender when pierced with a fork, about 10 minutes. Drain completely and transfer to a bowl.

In a small sauté pan over medium heat, warm the olive oil and swirl to coat the pan. Add the onion and sauté until soft and translucent, about 5 minutes. Add the curry powder, remaining 1 1/2 teaspoons of salt, and the sugar, and stir constantly until the curry is fragrant, 1 to 2 minutes longer. Remove from the heat.

Use a fork to mash the cauliflower into very small pieces. Add the onion mixture and stir to combine. Using a rubber spatula, stir in the yogurt, sour cream, parsley, nutmeg, cayenne, and a few grinds of pepper. Taste and adjust the seasonings. Transfer to a serving bowl and serve immediately.