| 1: Heat oven to 350°F (175°C) and adjust the rack to the middle position. |
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| 2: Whisk the flour, baking powder, and salt together in a medium bowl. |
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| 3: In a large bowl, beat the butter and sugar together on medium speed until light and fluffy, 3 to 6 minutes. |
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| 4: Beat in the eggs, one at a time, and then the vanilla and almond extracts until combined, about 30 seconds, scraping down the bowl and beaters as needed. |
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| 5: 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. |
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| 6: Press the dough into two 13- × 4-inch loaves on the prepared baking sheet, a few inches apart. |
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| 7: Bake until golden and just beginning to crack at the top, about 35 minutes, rotating the sheet halfway through the baking. |
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| 8: Let the loaves cool on the baking sheet for 10 minutes. Lower the oven temperature to 325°F (163°C). |
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| 9: Transfer the loaves to a cutting board and slice each on the diagonal into ½-inch-thick slices with a serrated knife. Lay the slices ½-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. |
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| 10: Transfer the biscotti slices to a wire rack and let cool completely before serving, about 1 hour. |
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| 11: Melt semisweet chocolate and "paint" one cut edge of each biscotti piece with the chocolate. |
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