Preheat your oven to 350°F (175°C). This ensures that your cookies bake evenly and thoroughly.
Line a baking sheet with parchment paper. This will help the cookies bake without sticking and make cleanup a breeze.
In a large mixing bowl, combine the Nutella, creamy peanut butter, and dark brown sugar. Using a whisk or electric mixer, blend until the mixture is smooth and creamy. Add in the egg and vanilla extract, continuing to mix until fully incorporated.
In a separate bowl, whisk together the all-purpose flour, baking soda, and pinch of salt (if using). Gradually add the dry ingredients to the wet mixture, stirring until just combined. Be careful not to overmix.
Chop the dark chocolate into chunks and fold them into the cookie dough. This will create delicious chocolate pockets throughout your cookies.
Using a cookie scoop or tablespoon, drop rounded balls of dough onto the prepared baking sheet, leaving enough space between each cookie to allow for spreading.
Place the baking sheet in the preheated oven and bake for 10-12 minutes, or until the edges are set but the centers are still soft. They will continue to firm up as they cool.
Once baked, remove the cookies from the oven and let them cool on the baking sheet for a few minutes before transferring them to a wire rack to cool completely. Enjoy your cookies warm, or store them for later!