1) Preheat the oven to 350°F. Lightly grease a large baking sheet; or line with parchment.
2) Toast the walnuts by spreading them in a single layer in a 9" x 13" (or similar size) pan, and baking in a preheated 350°F oven for 8 to 10 minutes, till they're a light golden brown.
3) Beat together the eggs, sugars, maple syrup, and maple flavor, if you're using it.
4) Add the melted butter, beating till smooth.
5) Mix in the flour, baking powder, and salt, then the nuts.
6) Divide the dough in half on a lightly greased or parchment-lined baking sheet.
7) Using your wet fingers, shape each half into a rough 10" rectangle, about 4" wide and 1/2" thick.
8) Using your wet fingers or a wet bowl scraper, smooth the top and sides of the rectangles. Sprinkle the top of each rectangle with 1 tablespoon maple sugar, if desired.
9) Bake the biscotti dough for 30 minutes. Remove from the oven, and cool for about 10 minutes; cooling the dough allows you to cut it more easily, with less crumbling.
10) Use a sharp chef's knife or serrated knife to cut the baked dough, slightly on the diagonal, into generous 1/2"-thick slices. Place the slices close together on the prepared baking sheet. If you can balance them upright (rather than laying them flat), so much the better; you won't have to turn them during their second bake.
11) Bake for about 20 to 25 minutes, till the biscotti's cut sides are beginning to brown. Remove them from the oven, and cool right on the baking sheet.
Yield: about 3 dozen 4" to 6" biscotti