1. In a large bowl, whisk together flour and salt. Pour 4 tablespoons melted butter over the flour mixture; reserve remaining 6 tablespoons butter for brushing paratha. Using your fingers, rub the butter into the flour until the mixture becomes moist and crumbly. Knead in 1/2 cup water, a little at a time, as needed, until a soft dough forms.

2. Transfer dough to a lightly floured surface and knead until smooth and elastic, about 5 minutes. Roll dough into a ball and transfer to a buttered bowl; cover bowl with plastic wrap and let stand at room temperature for 20 minutes.

3. Divide dough into six equal-size balls. Transfer one ball to a lightly floured surface, keeping remaining covered with a clean kitchen towel. Roll dough into a 6-inch circle. Using a pastry brush, brush surface of dough with butter and sprinkle with nigella seeds, if using. Fold dough in half, forming a semicircle. Brush surface of semicircle with butter; fold in half again to form a triangle. Gently roll out dough until paratha is just less than 1/4 inch thick.

4. Heat a large skillet over medium-low heat. Brush surface of paratha with butter and season with salt. Place, butter-side down, in skillet. Cook until bread begins to bubble, 2 to 3 minutes.

5. Brush exposed surface of paratha with butter and season with salt. Turn and cook until golden, 2 to 3 minutes. Transfer paratha to a plate. Repeat process with remaining dough, butter, and nigella seeds, if using.