- Preheat the oven to 350°F and line 2 baking trays with parchment paper.
- Using electric beaters or a stand mixer fitted with the whip attachment, whip the eggs and sugar on high speed until they hold a ribbon when the beaters are lifted, about 3 minutes. Beat in the vanilla.
- In a separate bowl, sift the !our, cocoa, baking powder and salt, and then fold this into the whipped eggs.
- Scrape this batter (which is the consistency of cake batter) into a piping bag with a large plain tip and pipe 3 rows of batter about 12 inches long and 1 ½ inches across onto each tray, leaving 2 inches between each row. Sprinkle the biscotti batter with the sliced almonds.
- Bake for about 16 minutes, until the tops of the biscotti appear dry (the cookies will still feel soft). Allow the cookies to cool almost to room temperature and reduce the oven temperature to 325°F.
- Using a chef’s knife, slice the biscotti into ¾ inch slices and return them to the baking tray.
- Bake the biscotti for about 20 minutes – the cookies may still feel a touch soft directly from the oven, but they will dry once cooled – if they are still soft at room temperature, return them to the oven for an additional 5 minutes. Once cooled, pack the biscotti into an airtight container.
The biscotti will keep for up to 3 weeks.