Whisk flour, salt, baking powder, and baking soda in medium bowl.
Using electric mixer, beat butter, 1 1/3 cups sugar, and lemon peel in large bowl until blended. Add 2 eggs, 1 at a time, beating just to blend after each addition. Beat in lemon juice, then flour mixture. Stir in walnuts.
Divide dough into 3 equal pieces. Place each piece on sheet of plastic wrap. Using plastic wrap as aid, form dough into 8-inch-long logs. Press logs slightly, flattening to 2 1/2-inch-wide logs. Enclose in plastic wrap and chill until firm, at least 3 hours and up to 3 days.
Position rack in upper third of oven and preheat to 325 degrees.
Line heavy large rimmed baking sheet with parchment paper.
Unwrap logs, leaving on plastic. Brush top of logs with egg glaze. Sprinkle with raw sugar. Lift logs from plastic and transfer to prepared baking sheet, spacing evenly. Bake until golden brown and just firm to touch, about 50 minutes.
Transfer to rack and cool completely. Reduce oven temperature to 300 degrees.
Line 2 heavy rimmed baking sheets with parchment paper. Using long serrated knife, carefully cut logs crosswise into 1/3-inch-thick slices. Arrange biscotti, cut-side down, on prepared baking sheets.
Bake cookies until golden brown around edges, about 20 minutes. Cool completely (biscotti will crisp as they cool). (Can be made 3 days ahead. Store in airtight container at room temperature. ).