Preheat oven to 350°F (175°C). Line a baking sheet with parchment paper and set aside.

In a medium bowl whisk flour, baking powder, and salt to combine. Set aside.

In a large mixing bowl, using a handheld or stand mixer fitted with a paddle or whisk attachment, stir butter, sugar, and oil on medium speed just until combined about 1 minute. Add eggs and vanilla and stir to combine.

Stir in dry ingredients just until combined. The cookie dough should be soft and slightly sticky. If the cookie dough is too sticky add another 1-2 tbsp of flour, 1 tbsp at a time. Fold in pistachios. Don't overmix at any step.

Divide the cookie dough in half and form 2 equal logs approximately 10x3-inches (26x8cm) in size and about 1-inch (2.5 cm) tall. Place on the prepared baking sheet about 4-inch (10cm) apart. Bake for 25 minutes. Then remove from the oven and let cool 10 minutes.

Then cut into 1-inch (2.5 cm) slices and set them upright on the cut sides about ¼-inch (0.6cm) apart. Bake for 8 minutes. Then turn them over and bake on the other side for 8 minutes. Remove from the oven and let cool for 5 minutes. Then transfer to a wire rack and let cool completely.

Place chocolate in a heatproof bowl and microwave for 2 minutes. Stir every 15-20 seconds to prevent seizing. Dip each biscotti into chocolate and place on parchment paper or a wire rack. Sprinkle with additional pistachios if preferred. Let dry. Store in an airtight container at room temperature for up to 2 weeks.