Combine all of the dry ingredients together ensuring the baking powder and psyllium powder are well mixed in.
Add the eggs, melted butter, orange zest and vanilla extract to the dry ingredients. Mix until well combined.
Use your hands to shape into a log approximately 25-30 cms/9-12" long. Round off the edges of your log to create a semi circle biscotti shape and compress your log to remove any air holes.
Bake at 160 C/ 320 F fan forced for 30 minutes or until the log has browned slightly on the outside.
Allow the biscotti log to cool to room temperature. Wrap in cling wrap and place in the fridge for about 1 hour. Slice your log into 1 cm/0.4" slices and place on baking paper without touching.
Reduce your oven down to 120 C/250 F fan forced and bake for approximately 20-25 minutes on each side, or until your biscotti has dried out. Turn the oven off and leave the door ajar and leave your biscotti in the oven to dry out further is it is still moist.
If you used erythritol in the recipe, the biscotti will continue to crisp up as they cool. Store your biscotti in an airtight container.
Add 1 teaspoon of cinnamon for a cinnamon spice flavor.Switch erythritol for 1/4- 1/2 cup of a monk fruit or stevia blend sweetener or adjust sweetener to suit your taste. 1/2 cup of coconut sugar can also be used for a paleo option.If you omit the psyllium husk/ xanthan powder you will need to handle your biscotti slices with extreme care as they will be more crumbly.For a dark chocolate drizzle/dip, melt 50 gms dark chocolate and dip the base of the cooled biscotti into the chocolate. You can also drizzle the biscotti with the dark chocolate. Allow to set by leaving on baking paper until the chocolate firms up.