Preheat the oven 350 F and line a baking sheet with parchment and set aside.
Pulse the flour, sugar, espresso powder, baking powder and salt in a food processor until combined. Add the butter and pulse until the mixture looks like sand.
Whisk the eggs, 1 tablespoon water and vanilla together in a large bowl until well mixed then add the flour mixture and stir until a crumbly dough forms. Press together and knead to a moist, uniform dough. Knead in the macadamia nuts.
Divide the dough in half and shape each into an 11-by-2-inch log on the prepared baking sheet, keeping 3-inches between the logs. Brush each log with egg white and sprinkle all over with sugar. Bake for 30 minutes.
Cool the logs for 5 minutes on the baking sheets and then transfer to a cutting board. Cut 1/2-inch thick slices using a sharp serrated knife. Return to the baking sheet and bake again, turning halfway though, until firm and browned, 25 minutes more. Transfer to a wire rack to cool. Store at room temperature in an airtight container for up to 2 weeks.
When measuring flour, we spoon it into a dry measuring cup and level off the excess. (Scooping directly from the bag compacts the flour, resulting in dry baked goods.)
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