Preheat the oven to 175°C/350°F. Line a baking sheet with parchment (baking) paper.

In a large bowl, whisk together the egg whites, sugar, oil, butter, cardamom seeds, baking powder and salt. Add the flour and mix until the ingredients come together. Scatter the pistachios and knead into dough.

Dump the dough onto a lightly floured work surface and divide the dough in half. Form two logs with 3-inch diameter. Transfer the logs onto the baking sheet, spacing them 5-inches apart. Pat to even out the surface of the logs.

Bake until firm to touch, about 28-30 minutes. Remove from the oven and let cool for 10 minutes (let the oven remain at 175°C/350°F). Carefully transfer the logs onto a cutting board. Using a serrated knife, cut crosswise into 1/2-inch thick slices. Arrange the slices cut side down on the baking sheet. Return to the oven and bake 8-9 minutes. Remove the tray from the oven and quickly turn the biscotti upside down and return to the oven for another 8-9 minutes.

Remove from the oven and let the biscotti cool completely on wire racks.

Store biscotti in an airtight container for up to two weeks.