Moosewood restaurant and adapted just a little. Try the sauce with other vegetables: broccoli, zucchini, asparagus, romanesco, beets, etc. EASY! The sauce was really good spooned over some leftover brown rice, too.
Steam the cauliflower for 15 to 20 minutes, or until tender. If you prefer, the cauliflower can be roasted or (pan) grilled. I pan grilled zucchini in place of cauliflower, cutting them up into 5" long by 1" thick pieces and lightly oiling them first.
While the cauliflower/vegetables cooks, sauté the onions in the oil in a small skillet until golden.
Add the curry powder and cook, stirring often, for another 2 minutes. Place the onion mixture in a bowl and allow to cool for about 10 minutes.
Transfer the onions to a food processor, add the yogurt, and puree until smooth. It may be necessary to add a splash of water to help the mixture to blend. Season with salt and pepper to taste.
When the cauliflower is done cooking, remove it to a serving platter, spoon on the curried yogurt sauce or serve the sauce in a bowl.