Preheat your oven to 140 degrees (fan).
Place the flour, baking powder and caster sugar in a bowl and mix.
Add the eggs bit by bit, mixing well after each addition. Carry on until a firm but not sticky dough is formed. You may not need to use all the eggs, I used about two and a half eggs.
Add the chopped pistachio, mango and lime oil and mix it well by hand until it is evenly distributed through the dough.
Place the dough on a floured work surface and knead it gently, then split it in half.
Roll each piece into a log shape, and place on a lined baking sheet, leaving a gap in between as they will spread.
Bake for 30-35 minutes.
Remove from the oven, check that the logs are set, and allow to cool for about ten minutes.
Use a serrated knife to cut the logs into thick slices, diagonally.
Return the slices to your baking tray, cut side up. Bake for 25 to 30 minutes, turning over half way through. Ensure the biscotti are cooked through before removing from the oven. Leave to cool.