Preheat oven to 425 degrees. Whisk together flour, salt, cardamom seeds, sugar, milk, 1/4 cup water, and the eggs in a large bowl. Let stand, covered, 20 minutes.
Heat a 12-inch cast-iron skillet in oven 10 minutes. Melt butter in skillet. Pour in batter; bake until puffed, about 25 minutes. Cut into wedges; serve with jam.