Mix flour and baking powder in medium bowl until well blended. Set aside. Mix sugar, butter, lemon juice and vanilla in large bowl. Stir in 3 of the eggs and pine nuts. Add flour mixture; stir until just blended. Cover. Refrigerate 30 minutes.
Preheat oven to 350°F. Divide dough in half. Form each half into a log, about 15 inches long and 2 inches in diameter, on parchment paper-lined baking sheet. With wet fingers, gently flatten top and smooth sides of logs. Brush logs with remaining beaten egg. Sprinkle tops and sides with sesame seed.
Bake 30 minutes or until pale golden brown. Cool logs on wire rack 15 minutes. Transfer to cutting board. Using a sharp serrated knife, cut logs diagonally into 1/2-inch thick slices. Place slices in single layer on ungreased baking sheets.
Bake 10 minutes for slightly crisp biscotti; bake 15 minutes for firmer biscotti. Cool on baking sheets 1 minute. Remove to wire racks; cool completely. Store in airtight container up to 5 days.