PREHEAT oven to 450° (bottom rack should be at least 6" above bottom of oven).

In a medium bowl, COMBINE flour, sugar, soda and salt; CUT in butter until mixture has a coarse crumb texture.

ADD buttermilk; STIR with fork until dough is moist and holds together.

On a floured surface, KNEAD dough lightly until smooth; DIVIDE in half.

GREASE 2 cookie sheets.

On sheet of floured wax paper, carefully ROLL half the dough into a thin, 10" circle, SPRINKLING with flour if necessary.

INVERT dough onto prepared cookie sheet; REMOVE wax paper.

REPEAT previous 2 steps for remaining dough.

BRUSH dough with egg white; SPRINKLE with seeds.

BAKE until golden, about 10 to 12 minutes; SWITCH positions of cookie sheets half way through baking to assure even browning.

TRANSFER to wire racks to cool.