These crackers give new dimension to a wine-and-cheese party.
Heat over to 350 degrees. In the bowl of a food processor, pulse flours, salt, pepper, sugar, and 2 tablespoons caraway seeds to combine. Add butter; pulse until mixture resembles coarse meal. Add onion; pulse until well combined, about 30 seconds. With machine running, gradually add between 1 and 2 tablespoons cold water, until dough comes together and is stiff.
Transfer dough to a lightly floured surface; roll out to a 14-by-16-inch rectangle, 1/16 inch thick. Roll out as thinly as possible. Cut into 2-by-3 1/2 inches rectangles.
Brush egg white over dough, and sprinkle with remaining 2 tablespoons caraway seeds and coarse salt. Pierce crackers liberally with a fork. Bake on ungreased baking sheet about 20 to 25 minutes, until firm to the touch, rotating baking sheet if needed for even cooking. Let cool on wire rack. Store in airtight plastic container.