Heat your oven to 320°F and grease a 9x13 inch baking dish (or 8x8 inch for thicker bars). I recommend using parchment paper for easy removal after baking.

Chop the 4.5 oz chocolate bar into small pieces and combine with butter in a microwave-safe bowl. Microwave in 30-second intervals, stirring between each interval, until completely melted and smooth—this usually takes 1-2 minutes total. The key is not to overheat, which can scorch the chocolate.

Add sugar to the melted chocolate mixture from Step 2 and stir well to combine. Add room temperature eggs one at a time, stirring thoroughly after each addition—this helps them incorporate smoothly and build a cohesive batter. Stir in the vanilla extract until fully mixed. I like to use room temperature eggs because they blend more evenly into the batter, creating a smoother texture.

In a separate small bowl, whisk together flour, cocoa powder, instant espresso powder, and salt—this distributes the espresso powder evenly throughout the batter and prevents cocoa clumps. Fold the dry mixture into the wet ingredients from Step 3 until just combined, then gently fold in the shredded zucchini and 1 cup chocolate chips. Don't overmix; stop as soon as you don't see streaks of flour.

Pour the batter into your prepared pan from Step 1 and smooth the top gently. Scatter the 2 tablespoons of chocolate chips over the surface and finish with a light pinch of flaky sea salt—the salt enhances the chocolate flavor and adds a subtle sophistication. Bake for 25 minutes, until a toothpick inserted in the center comes out with just a few moist crumbs (not completely dry, as these bars should be fudgy).

Remove the pan from the oven and let the bars cool completely in the pan on a wire rack—this helps them set properly and makes slicing much easier. Once fully cooled, cut into squares and serve. I find waiting until they're completely cool prevents crumbling and gives you cleaner, more attractive pieces.