Step 1

Preheat the oven to 325 degrees F (165 degrees C), with racks in the upper and lower third. Line 2 large baking sheets with parchment paper.

Step 2

Whisk flour, sugar, and baking soda together in a large bowl. Set aside.

Step 3

Beat butter using the paddle attachment of an electric mixer on medium-high speed until fluffy, about 1 1/2 minutes. Gradually add flour mixture and beat on medium-low speed until just combined, about 2 minutes. Divide dough into quarters.

Step 4

Working with one quarter at a time, roll dough between 2 large sheets of parchment until 1/8-inch thick. Chill between the parchment on a baking sheet until firm, about 15 minutes.

Step 5

Cut out enough cookies to fill the 2 baking sheets with 2-by-1 1/2-inch rectangles or your desired shapes. Arrange 1 inch apart on the sheets. Brush tops of cookies with some of the egg and sprinkle evenly with a portion of turbinado sugar. Keep unused dough in the fridge.

Step 6

Bake cookies, 2 sheets at a time, until pale golden, 14 to 15 minutes, rotating pans after 7 minutes. Let cookies cool on sheets for about 5 minutes, then carefully move them to a wire rack to cool completely before dipping. Cut, brush, and bake the remaining cookie dough in the meantime.

Step 7

Place chocolate in a microwave-safe bowl. Microwave on high for 30-second intervals until melted and smooth, about 1 1/2 minutes. Either dip cookies halfway in chocolate mixture and let excess drip off, or use a fork and drizzle chocolate Jackson Pollack-style over cookies over a parchment-lined baking sheet. Sprinkle salt over chocolate. Let rest until chocolate sets, about 1 hour.