Heat the oven 180ºC. Line 2 large baking trays with baking paper.
Weigh out all the dry ingredients and very roughly chop the chocolate and almonds into chunks.
Put the flour, cocoa, sugar, the chocolate, baking powder and ½ teaspoon of sea salt into a food processor. Pulse until the mixture resembles fine crumbs.
Beat together and add the eggs and vanilla and pulse until the dough just comes together.
(You could do all this with your hands, mix dry ingredients into a bowl, add the chopped chocolate, and then, add the beaten eggs and vanilla and mix with your hands until in becomes a kind of dry dough)
Tip onto a floured surface, add the almonds and work the dough to a ball.
Divide the dough into 2 pieces and shape each piece into a log approximately 3cm x 30cm.
Carefully transfer the dough logs onto one of the baking trays and bake for 25 minutes, until hard on the outside but not all the way through – this will allow you to slice the biscotti without the log crumbling. Leave to cool in the tin.
With a serrated knife, cut the biscotti diagonally into 1.5cm-thick slices. Arrange the slices on the baking sheets and bake for 15 to 20 minutes, until firm. The biscuits may still seem a little soft but they will firm up as they cool.
These will keep in an airtight container for a few days.