Samosas

In medium bowl, whisk together flour, nigella seeds, and salt. Add 2 tablespoons oil and, using fingertips, blend until mixture resembles fine bread crumbs. Add 3/4 cup warm water and mix with fork until dough just comes together. Transfer to lightly floured surface and knead until smooth and elastic, about 10 minutes. Lightly oil medium bowl, form dough into ball, and place in bowl. Cover with towel and set aside to rest for 30 to 40 minutes.

In large pot, cover potatoes with cold water. Bring to boil, then reduce heat and simmer, covered, until tender, about 20 minutes. Drain and, when cool enough to handle, finely dice.

In large bowl, combine diced potatoes, green onions, chiles (if using), cilantro, cumin seeds, ground cumin, chile powder, and salt. Mix with fork, mashing potatoes slightly to incorporate all ingredients.

Divide dough into 12 equal portions. Roll portions into balls. On floured surface using floured rolling pin, roll out 1 ball into 6-inch circle. Cut circle in half. Fold 1 corner of semicircle up and over middle. Fold second corner over to make triangle, and pinch corners of triangle to seal (leave rounded side open). Hold triangle in your hand with open rounded side facing up and let dough fall open to make cone. Fill cone with approximately 2 tablespoons potato mixture, then pinch along rounded side to seal. Repeat with remaining dough and filling.

In heavy, deep skillet over moderate heat, heat 2 inches oil until thermometer registers 360°F. Working in batches (return oil to 360°F between batches), fry samosas until golden brown, 1 to 2 minutes per side. Drain on paper towels. Serve warm with yogurt.