1. Preheat your oven to 350 F (175 C). Lightly grease and flour an 8×8 inch baking pan, or line it with parchment paper, leaving an overhang on two sides to easily lift the brownies out later.

2. In a medium-sized mixing bowl, melt the butter. Add the granulated sugar to the melted butter and whisk until well combined. Stir in the eggs one at a time, mixing well after each addition, until the mixture is smooth and glossy. Incorporate the vanilla extract and the sourdough discard, mixing until just combined. The mixture might look a little lumpy from the sourdough, which is perfectly fine.

3. In a separate, smaller bowl, whisk together the all-purpose flour, unsweetened cocoa powder, instant espresso powder, and salt. Ensure there are no lumps in the cocoa powder or flour for a smooth batter.

4. Gradually add the dry ingredient mixture to the wet ingredient mixture, stirring with a spatula or wooden spoon until just combined. Be careful not to overmix; overmixing can lead to tough brownies. A few streaks of flour are okay. If using, gently fold in the chocolate chips.

5. Pour the brownie batter into your prepared 8×8 inch baking pan and spread it evenly with a spatula.

6. Bake for 25-30 minutes, or until a toothpick inserted into the center comes out with moist crumbs, but not wet batter. The edges should be set, and the center might still look slightly soft, which will ensure a fudgy texture.

7. Remove the pan from the oven and let the brownies cool completely in the pan on a wire rack before slicing. This allows them to set properly and prevents them from crumbling. For an extra fudgy experience, you can even chill them in the refrigerator for an hour before cutting.