Preheat your oven to 350 degrees. In a large bowl, combine the flour, salt and baking powder. Stir very well so that the baking powder is evenly distributed.
In a second bowl, combine the eggs, sugar, butter, vanilla extract, almond extract, cinnamon, nutmeg and lemon zest. Whisk it all together until it is evenly incorporated and has a light creamy appearance (see photos below).
Pour the wet mixture into the dry flour mixture. Stir until it is evenly combined and you have a wet dough that is similar to cookie batter. Fold in the sliced almonds and dried cranberries (if using).
On a baking sheet lined with parchment paper, form two semi-flat logs about 2 inches wide and 12 inches long (see photos below). Make sure the logs are a few inches apart because they will expand slightly while baking. Bake at 350 degrees for 35 minutes.
Using a spatula, remove the logs to a cutting board. Cut the logs into 1 inch thick slices on a diagonal (this makes the biscotti longer). A serrated knife works best for slicing the biscotti. Place the slices back on the baking sheet. Bake the slices for 5-7 minutes more on each side (depending on how crisp you like them). Larger, thicker logs will require a more time to crisp up.
Allow the biscotti to cool. Enjoy the biscotti plain or dunked in coffee!