Biscotti are twice-baked, which gives them their firm, dry texture and makes them well suited for dipping in coffee or tea. This version adds finely ground espresso and roughly chopped walnuts to the dough for a bitter, earthy depth of flavor. The two baking rounds take about 50 minutes in total.
Preheat the oven to 350°F (175°C). Line a baking sheet with parchment paper.
In a large mixing bowl, whisk together the flour, baking powder, and salt.
In a separate bowl, use an electric mixer to beat the sugar and eggs on medium speed until thick and pale, about 3 minutes.
Mix in the espresso powder and vanilla extract until combined.
Gradually add the flour mixture, beating on low speed until just combined. Stir in the toasted walnuts.
Transfer the dough onto the prepared baking sheet, shaping into a log about 12 inches long and 3 inches wide. Smooth the top and sides with a spatula.
Bake for 25 minutes or until lightly golden and firm to the touch. Remove from oven and let cool slightly on a wire rack, about 10 minutes.
Reduce the oven temperature to 325°F (160°C).
Using a serrated knife, cut the log into 1/2-inch slices. Arrange the slices cut side down on the baking sheet.
Bake for another 20 minutes, flipping the biscotti halfway through baking. They should be dry and crispy.
Remove from oven and cool completely on a wire rack.
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Notes
For a mocha twist, dip the cooled biscotti halfway in melted dark chocolate and allow to set. If you prefer a sweeter biscotti, increase the sugar to 1 1/4 cups.