Whisk your dry ingredients in a bowl. Add the pecans (leaving some aside for the next step!), chocolate and raisins and stir to coat with flour.
Put the extra pecans and sugar into a food processor or blender and process to grind the nuts finely.
Transfer the pecan sugar mixture to a separate bowl. Combine with brown sugar, melted butter, vanilla, whole eggs, and egg yolk. Whisk thoroughly and then pour into the bowl of dry ingredients.
Place the pecan biscotti dough onto a generously floured surface. Gently knead it a few times to bring it together.
Divide the biscotti dough in half and shape each portion into a log. Put the logs onto a parchment lined baking sheet with a gap of about 2 inches between them.
Lightly beat egg white and brush it over the tops of the loaves, then sprinkle generously with extra granulated or turbinado sugar.
Bake the pecan biscotti loaves until they’re cooked through and ends are just starting to brown.
Let the biscotti cool on the baking sheet for about 15 minutes. Then slice.
Arrange pecan biscotti slices on the lined baking sheet. Bake again until dry and firm.