Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper to make cleanup a breeze.
In a large mixing bowl, cream together the granulated white sugar and softened salted butter until light and fluffy. This should take about 2-3 minutes with a hand mixer or stand mixer.
Beat in the two large eggs one at a time, ensuring each is fully incorporated before adding the next. Then, mix in the instant espresso powder for an added depth of flavor.
In a separate bowl, whisk together the all-purpose flour, unsweetened cocoa powder, baking powder, and a pinch of salt. Gradually add this mixture to the wet ingredients, mixing until just combined.
Gently fold in the dark chocolate chunks and semi-sweet chocolate chunks, allowing them to distribute evenly throughout the dough.
Transfer the dough to the prepared baking sheet. With floured hands, shape the dough into a log about 12 inches long and 3 inches wide. Flatten the top slightly for even baking.
Bake the log in the preheated oven for 25-30 minutes, or until firm to the touch. Remove it from the oven and allow it to cool for about 10 minutes.
Once the log is cool enough to handle, use a sharp knife to slice it diagonally into 1-inch thick pieces.
Lay the slices cut-side down back on the baking sheet. Bake for an additional 15-20 minutes, flipping them halfway through, until they are crisp and dry.
Remove the biscotti from the oven and let them cool completely on a wire rack. These delightful treats are now ready to be enjoyed, dunked in coffee, or shared with loved ones!