Step 1

In the bowl of a food processor, pulse flour, baking powder, and salt until combined. Add butter; pulse until mixture resembles coarse meal. Transfer to a medium bowl; stir in buttermilk and 1 cup sesame seeds until mixture forms a dough. Divide into quarters; wrap in plastic. Chill 20 minutes.

Step 2

Preheat oven to 350 degrees. In a small bowl, whisk together egg, sugar, and soy sauce. Transfer one piece of dough to a lightly floured work surface; roll out into a rectangle about 1/8 inch thick. Use a sharp knife or pizza wheel to cut into strips, about 3/8 inch wide and 10 inches long. Brush strips with egg mixture; sprinkle with remaining 1/4 cup sesame seeds.

Step 3

Arrange strips on a parchment-lined baking sheet. Bake until just golden, 15 to 20 minutes. Transfer to a wire rack to cool. Repeat with remaining dough.