Sometimes called black onion seed or nigella, kalonji is a small teardrop-shaped seed that looks like black sesame. Widely used in Indian cooking to give a nutty nip to curries and breads, peppery kalonji seeds should be stored in airtight jars and out of direct light.
Here's a recipe for Sweet Potato Masala adapted from Bharti Kirchner's cookbook, Bold Vegetarian (Harper Perennial). Peel and chop 1 lb sweet potatoes into 1-inch cubes, then steam them for 15 to 18 minutes till tender. While they're cooking, put 10 chopped sun-dried tomatoes in a microwavable dish with 1 cup water, cover and nuke for 2 minutes. Drain, reserving the tomato water. In a non-stick skillet over high heat, dry-roast 2 whole dried chilies and 1/4 tablespoon kalonji seeds, stirring constantly until the chilies darken and some of the seeds split open. Lower heat and add 3 large minced garlic cloves, stirring so the garlic doesn't burn. Add 2 or 3 tablespoons tomato water, followed by 1/4 tablespoon ground turmeric, 1 tablespoon ground cumin, 3/4 tablespoon sugar, 1/8 tablespoon cayenne and 1/4 tablespoon salt. Simmer this spice mixture for a minute, adding more tomato water if necessary. Add drained sun-dried tomatoes and whatever remains of the tomato water and simmer another 7 to 10 minutes, mashing the tomatoes occasionally until a thick sauce forms. Mash the sweet potatoes and add to the tomato sauce, simmering for another 5 minutes. Garnish with fresh coriander. Serves four.