Cool completely on a wire rack. Dip the flat side of each biscotti into melted white chocolate or candy melts. Place on parchment paper to set. Drizzle additional chocolate over the tops if desired. Allow chocolate to fully set before storing or freezing.

Preheat the oven to 350 degrees F. Line a large baking sheet with parchment paper.

In a medium bowl, whisk together flour, baking powder, and salt. Set aside.

In a large bowl using a handheld electric mixer, or in the bowl of a stand mixer fitted with the paddle attachment, beat sugar and eggs until light in color and slightly thickened, about 3 minutes. Mix in vanilla extract and lemon zest until combined.

Add the flour mixture to the wet ingredients and mix on low speed just until combined. The dough will be thick and slightly sticky. Do not overmix.

Divide dough evenly into two portions. On the prepared baking sheet, shape each portion into a log about 13 inches long and 3 to 4 inches wide. Gently pat the tops smooth and slightly flatten the logs.

Bake for 35 minutes, until golden brown and beginning to crack on top. Remove from the oven and cool for at least 10 minutes. For even cleaner slices, wrap and wait until the next day to slice.

Reduce oven temperature to 325 degrees F. Using a serrated knife, slice logs diagonally into ¾-inch thick pieces. Thicker slices will be slightly softer in the center. Thinner slices will be extra crisp. The end pieces are perfect for nibbling.

Place slices cut side up in a single layer on the baking sheet. Bake for 15 minutes, flipping halfway through, until dry and crisp.