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

Place the chocolate chips and butter in a microwave-safe bowl and melt in 20-30 second intervals, stirring each time until smooth.

In a separate bowl, whisk the egg, granulated sugar, and vanilla extract vigorously for 1-2 minutes until slightly pale, thickened, and glossy (this step is essential for creating the shiny crackly top).

Slowly pour the warm melted chocolate mixture and sourdough discard into the egg mixture, whisking until smooth and fully incorporated.

Add the cocoa powder, flour, baking powder, and salt to the mixture and fold gently with a spatula until a thick batter forms.

Fold in the chocolate chunks evenly throughout the dough.

Let the dough rest for 15 minutes at room temperature to thicken slightly and deepen the flavor.

Scoop tablespoon-sized portions of dough onto the prepared baking sheet, leaving space between cookies.

Bake for 10-12 minutes until the cookies develop shiny crackled tops and the edges are set.

Remove from the oven and allow the cookies to cool on the baking sheet for 10 minutes.

Transfer the cookies to a cooling rack and allow them to cool completely before serving.