Beat the eggs, sunflower oil, vanilla, and sugar with an electric mixer until well combined.
Add the flour, salt, cinnamon, mixed spice, orange zest, and baking powder and mix until a sticky dough forms.
Empty the dough onto a floured work surface and knead until smooth and no longer sticky.
Divide the dough into two and roll each half into a log about 30 cm long. Place them on a lined baking tray and chill.
Preheat the oven to 180°C (350°F). Bake the logs for 20 to 30 minutes until golden.
Let cool slightly, then reduce the oven temperature to 100°C (212°F).
Slice the biscotti diagonally and lay them back on the baking sheet.
Bake for an additional 30 minutes until dry and crisp.
