Preheat oven to 350 degrees.
Toast the anise seed in a small saute pan over medium heat until the seeds begin to color and become fragrant, about 3-5 minutes. Quickly remove them from the heat and the pan to stop them from cooking.
Combine the eggs and sugar in the bowl of a standing mixer with the paddle attachment (or in a large bowl if mixing by hand). Beat until the eggs and sugar are thoroughly combined. Mix in the anise seed, lemon juice and melted butter. If adding nuts, include them in now.
Add the flour, one cup at a time with the mixer on low. If doing this by hand, after 5 cups the dough is going to get very thick and harder to mix. You may have to incorporate the last cups with your hands.
On a floured surface, divide the dough into 3 parts. You will need at least 2 baking sheet pans, preferably 3. Form each part into a long roll about 2" high and as long as a typical cookie sheet. Place the roll on a cookie sheet lined with either a Silpat Baking Mat or parchment paper. Then press down with your hand to from a loaf about 4" across and 1" high.
Bake the loaves for 20-25 minutes until they are firm and a skewer comes out clean from the center. Remove them from the oven (but leave it on) and let the loaves cool for about 10 minutes.
Slice each loaf on the diagonal in 1/2" to 3/4" slices and lay out the biscotti on an unpapered pan. Don't worry if the cookies are slightly sticky in the center, they will finish cooking when they go back in the oven. But if they are more sticky then not in the center, you might want to put the whole loaf back in for a few more minutes.
Place the pan on the bottom rack of the oven and toast the cookies for about 15 minutes or until they are light brown on the bottom. Turn the cookies over and toast for another 5 minutes or until the other side is light brown. Repeat with the other trays of cookies. You can save a little time by putting the other trays in the oven to start them drying out, but they really toast best on the bottom rack.