INSTRUCTIONS
1. Adjust an oven rack to the middle position and heat the oven to 350°F. Line a large baking sheet with parchment paper. Whisk the flour, baking powder, and salt together in a medium bowl.
2. In a large bowl, beat the butter and sugar together using an electric mixer on medium speed until light and fluffy, 3 to 6 minutes. Beat in the eggs, one at a time, then the vanilla and almond extracts until combined, about 30 seconds, scraping down the bowl and beaters as needed.
3. Reduce the mixer speed to low and slowly mix in the flour mixture until combined, about 30 seconds. Mix in the almonds and zest (if using) until just incorporated.
4. Press the dough into two 135. by 2-inch loaves on the prepared baking sheet, spaced about 3 inches apart. Bake the loaves until golden and just beginning to crack at the top, about 35 minutes, rotating the baking sheet halfway through the baking.
6. Let the loaves cool on the baking sheet for 10 minutes. Lower the oven temperature to 325°F.
7. Transfer the loaves to a cutting board and slice each on the diagonal into 1/2-inch-thick slices with a serrated knife. Lay the slices about 1/2-inch apart on the baking sheet and bake until crisp and golden brown on both sides, about 15 minutes, flipping the slices over halfway through the baking. Transfer the biscotti spices to a wire rack and let cool completely before serving, about 1 hour.
