In a mixing bowl, cream together:
1 stick (1/2 C) soft butter
1 cup sugar
3 eggs
2 Tblsp. fresh lemon juice
1 Tblsp. grated lemon zest
Stir in:
3 cups flour
2 Tblsp. poppy seeds
1 tsp. baking soda
1 tsp. baking powder
1/8 tsp. salt
Divide the dough into 4 equal parts. Form each part into a cylinder (flour your hands to keep the dough from sticking) and place them on baking sheets (2 per sheet, leaving room between them). Flatten each cylinder so that it becomes a rectangle, approx. 1/3" high, 2" wide, and 6-8" long. Bake for approx. 20 minutes, or until the rectangles become slightly firm and golden. Remove from the oven, let cool for a minute and then cut into slices - making each biscotti about 1/3-1/2" wide. Separate them and keep them on the same baking sheet, leaving space between them. Return to the hot oven and continue to bake another 10-15 minutes (depending on how dry/crunchy you want them). Remove from the oven and let them cool completely.
Make a glaze by mixing 2 Tblsp. soft butter, 2 Tblsp. grated lemon zest, 2-3 cups powdered sugar and enough lemon juice to make a spreadable glaze. Push the biscotti back together (so it looks like the rectangle you had pre-baking) and with a pastry brush, liberally brush the glaze over the tops of the biscotti. Let them dry completely. Yum!
