Preheat the oven to 350°F/Gas Mark 4.
Beat together the eggs with caster sugar, add in the butter and mix until light and fluffy, then pour in the orange extract along with the ground almonds. Zest in the fresh orange into the mix and mix together.
Next sift the flour and baking powder mix well. Lastly add the fresh orange juice into the mixture and blend together.
With (really) floury hands, divide the dough in half and shape each half into a log 7.5cm in diameter. Place the logs on to a baking trays and bake in the pre-heated oven for 30 minutes or until firm to the touch. Leaving the oven on, transfer the loaves to a cutting board. Using a knife, cut each loaf into 1cm slices. Arrange the slices in one layer on a baking tray and return to the oven & bake for ten minutes. Turn the biscotti over and bake for a further ten minutes on the other side. Transfer the biscotti to wire racks to cool.
Place a glass bowl suspended over a pan of simmering water, and melt chocolate in the bowl. Once melted remove the bowl from the pan and stir in the orange extract.
Dip the biscotti into the chocolate, leaving half of the biscotti without chocolate. Leave to cool.