Add egg, baking powder, salt and lemon juice. Mix well.
Switch to beater attachment- Add the zest, mix, then add flour slowly while mixing.
When well mixed, add the walnuts and mix until evenly distributed.
Split the dough in half, and roll each into a log. Place on parchment lined baking sheet. Press and mold with your hands, until approx. 3" wide and 1" thick.
Bake logs for 30 min. Remove and reduce oven temp. to 325°.
Allow the logs to cool, then slice into ½" thick cookies.
Place the cookies back on the parchment lined baking sheet and bake for 15 minutes.
Store the Lemon-Walnut Biscotti in an airtight container.