This is what prompted my grandfather, last Christmas, to tell my mother and me that we should open a bakery.
Like Smitten Kitchen says, these are supposed to make 3 dozen, but my batch also yielded at least 45. Just depends on whether you actually slice them 1/2″ wide.
3 1/4 cups all purpose flour
1 tablespoon baking powder
1/3 teaspoon salt
1 1/2 cups sugar
10 tablespoons (1 1/4 sticks) unsalted butter, melted
3 large eggs
1 tablespoon vanilla extract
1 tablespoon orange liqueur
1 tablespoon orange zest
1 cup whole almonds, toasted, coarsely chopped or sliced almonds
1 large egg white
Position rack in center of oven and preheat to 350°F. Line baking sheet with parchment paper. Sift flour, baking powder and salt into medium bowl. Mix sugar, melted butter, 3 eggs, vanilla extract, orange liquer and zest in large bowl. Add flour mixture to egg mixture and stir with wooden spoon until well blended. Mix in almonds.
Divide dough in half. Using floured hands, shape each dough half into 13 1/2-inch-long, 2 1/2-inch-wide log. Transfer both logs to prepared baking sheet, spacing apart. Whisk egg white in small bowl until foamy; brush over top and sides of each dough log.
Bake logs until golden brown (logs will spread), about 30 minutes. Cool logs completely on sheet on rack, about 25 minutes. Maintain oven temperature.
Transfer logs to work surface; discard parchment paper. Using serrated knife, cut logs on diagonal into 1/2-inch-wide slices. Arrange slices, cut side down, on same baking sheet. Bake 12 minutes. Turn biscotti over; bake until just beginning to color, about 8 minutes. Transfer to rack and cool.
Do ahead: Can be prepared one week ahead, though mine have kept even longer. Store in airtight container at room temperature.