Vegetable oil, for the baking sheet
9 oz. (2 cups) unbleached all-purpose flour
3/4 cup plus 1 Tbs. granulated sugar
2 tsp. finely grated lemon zest
1/2 tsp. baking powder
1/4 tsp. table salt
3/4 cup (4 oz.) whole, skin-on almonds, toasted
3 large eggs, beaten
1 tsp. pure vanilla extract
1/2 tsp. pure almond extract
Position a rack in the center of the oven and heat the oven to 350°F. Lightly oil a large rimmed baking sheet.
Put the flour, 3/4 cup of the sugar, lemon zest, baking powder, and salt in a stand mixer fitted with the paddle attachment. Mix on low speed until combined, about 30 seconds. Add the almonds and mix to combine and break the nuts into pieces about 1/3 to 1/4 their original size, 1 to 2 minutes. Reserve 1 Tbs. of the beaten eggs in a small bowl. Add the remaining eggs and both extracts to the mixer. Mix on medium-low speed until a soft, sticky dough forms, about 2 minutes.
Turn the dough out onto a clean work surface and pat it into a 5-inch disk; halve the disk. Lightly moisten your hands with oil or water, then squeeze and pat one piece of dough into a log. Lay the log lengthwise on one side of the prepared baking sheet. Stretch and pat the dough into a flat loaf that’s about 12 inches long and 2 to 2-1/2 inches wide. Repeat with the remaining dough on the opposite side of the sheet; leave at least 2 inches of space between the loaves.
Mix the reserved beaten egg with 2 tsp. water. Lightly brush the loaves with the egg wash and sprinkle with the remaining 1 Tbs. sugar.
Bake until pale golden around the edges and just set, 20 to 25 minutes. (There will be cracks on the surface, which is OK.) Reduce the oven temperature to 300°F.
Set the baking sheet on a cooling rack. Gently slide an offset spatula under each loaf to loosen it. Let cool on the sheet for 5 minutes, then transfer to the rack and let cool for 20 to 30 minutes longer.
Transfer the loaves to a cutting board. Using a sharp knife, cut the loaves on the diagonal into 1/2-inch-thick slices. Arrange the slices, cut side up, on the baking sheet; it’s fine if they fit snugly. Bake for 10 minutes, then flip and bake until golden, about 10 minutes more. Transfer the biscotti to the rack and cool completely; they will become firm and crunchy as they cool.