Indian-Spiced Cauliflower Dip

1 head cauliflower (about 1 1/2 pounds), broken into small florets

1 3/4 tsp. coarse salt , divided

1 Tbsp. canola oil

1 tsp. black mustard seeds

1 medium yellow onion , finely diced

1 Tbsp. curry powder

1 Tbsp. sugar

1 cup plain, low-fat yogurt

1/4 cup reduced-fat sour cream

1/3 cup chopped cilantro

1/4 tsp. nutmeg

1/4 tsp. cayenne pepper

1/4 tsp. freshly ground black pepper

Bring a large pot of water to a boil. Add cauliflower and 1/4 teaspoon salt. Partially cover pan and simmer until tender, about 10 minutes. Drain.
In a small sauté pan over medium heat, warm oil and coat pan. Add mustard seeds, cover, and cook until seeds stop popping, about 30 seconds. Add onion and sauté until translucent, about 5 minutes. Add curry, 11/2 teaspoon salt, and sugar, and cook until fragrant.
Mash cauliflower and add onion mixture and remaining ingredients.