1. Preheat your oven to 350°F (175°C). Line an 8×8-inch baking pan with parchment paper, leaving a 1–2-inch overhang on two sides for easy removal.

2. In a small microwave-safe bowl or over low heat on the stove, melt the butter until just liquid. Set aside to cool for 1–2 minutes.

3. In a large mixing bowl, whisk together the melted butter and light brown sugar vigorously until the mixture is smooth and no large clumps remain, about 30–45 seconds.

4. Crack the room-temperature egg into the sugar mixture. Add the sourdough discard and vanilla extract. Whisk until the batter is glossy and homogeneous, scraping down the sides of the bowl as needed.

5. In a separate medium bowl, whisk together the all-purpose flour, baking powder, and salt until evenly combined.

6. Pour the dry ingredients into the wet ingredients. Using a silicone spatula, fold gently just until there are no visible streaks of flour—do not overmix to keep the blondies tender.

7. Reserve ¼ cup of the chocolate chips for the topping, then fold the remaining ½ cup into the batter, distributing evenly.

8. Transfer the batter to the prepared pan. Use the spatula to spread it into an even layer, pressing into all corners.

9. Evenly sprinkle the reserved ¼ cup of chocolate chips over the top of the batter, gently pressing them in so they adhere.

10. Bake on the middle rack for 20–25 minutes, or until the edges are set and golden and the center appears just set but still slightly gooey when jiggled.

11. Remove from the oven and place the pan on a wire rack. Allow the blondies to cool completely in the pan, at least 20 minutes, so they finish cooking and firm up for clean slicing.

12. Once cooled, lift the bars out using the parchment overhang. Transfer to a cutting board and slice into 9 or 12 squares with a sharp knife, wiping the blade between cuts for neat edges.