Preheat oven to 400°. In a small skillet over medium heat, melt 1 tablespoon butter. Add leeks; cook until tender, 6-7 minutes. Cool.
Whisk together flour, baking powder, salt and baking soda. Cut in remaining butter until mixture resembles coarse crumbs. Stir in leeks, sour cream and water just until moistened. Turn onto a lightly floured surface; knead 8-10 times.
Pat or roll out to ½-in. thickness; cut with a floured 2-½-in. biscuit cutter. Place in a cast-iron or other ovenproof skillet. Bake until golden brown, 12-16 minutes. Serve warm.
