Preheat the oven to 180°C (160°C fan). Spread the almonds on a baking tray and toast for 9–10 minutes until lightly golden. Set aside to cool completely.
Melt the butter and leave it to cool slightly so it is still liquid. In a large mixing bowl, whisk together the melted butter and sugar. Add the eggs, almond extract, and vanilla extract, then whisk until well combined. Add the flour, baking powder, salt, and orange zest. Mix with a fork until a shaggy dough forms.
Stir in the cooled toasted almonds and mix until evenly distributed. The dough should resemble a firm cookie dough. If it feels too sticky to handle, add a little extra flour. If the dough is warm and soft, chill it in the fridge for 10–15 minutes.
Divide the dough in half and shape each portion into a log approximately 6cm wide. Place the logs well apart on a baking tray lined with a silicone mat or baking paper, as they will spread during baking. Bake for 30 minutes at 180°C until lightly golden. Remove from the oven and allow the logs to cool completely, about 1 hour. The cooler they are, the easier they will be to slice.
Using a sharp serrated knife, slice the logs diagonally into 6–7mm thick biscotti.
Reduce the oven temperature to 150°C. Arrange the slices cut-side down on a lined baking tray. Bake for 12 minutes, then turn the biscotti over and bake for a further 12 minutes.
Leave the biscotti to cool completely on the tray. They will become deliciously crisp as they cool.