Preheat your oven to 325°F and line a 9x13 inch baking dish with parchment paper, allowing it to overhang slightly on two sides for easy removal later. While the oven preheats, melt the butter in a small saucepan over medium heat. Once melted, continue cooking for 8-10 minutes, swirling occasionally, until the milk solids turn golden brown and develop a nutty aroma—this is the critical flavor-building step that distinguishes these brownies. Pour the browned butter (including all those precious brown bits) into a bowl and set aside to cool slightly.

While the butter cools, whisk together the flour, cocoa powder (sifted to remove lumps), cornstarch, espresso powder, baking powder, and salt in a medium bowl. Set this dry mixture aside. I like to sift the cocoa powder first because it ensures there are no lumps that will create bitter pockets in the final brownies.

Pour the slightly cooled browned butter into a larger mixing bowl and add the chocolate chips. Stir constantly for about 1-2 minutes until the residual heat melts the chocolate completely and creates a smooth, glossy mixture. The warm butter will melt the chips without requiring additional heat.

In a separate bowl, whisk together the room-temperature eggs and both sugars (granulated and brown) vigorously for about 4 minutes. This aerating step is essential—it creates a light, fluffy structure that will give the brownies a tender crumb and fudgy texture. The mixture should become slightly paler and have increased volume. Pour in the vegetable oil and vanilla extract, then gently fold in the chocolate mixture from Step 3 until fully combined.

Gently fold the dry ingredient mixture from Step 2 into the wet ingredients until just combined—do not overmix, as this can develop gluten and create a dense, cake-like texture. Fold carefully with a spatula, working from the bottom of the bowl upward, until no white streaks of flour remain.

Pour the batter into the prepared baking dish and spread evenly. Bake for 45-50 minutes at 325°F until a toothpick inserted into the center comes out with just a few moist crumbs clinging to it—do not overbake, as these brownies should be fudgy and moist rather than cakey. The edges may pull slightly away from the pan when fully baked.

Allow the brownies to cool in the pan for at least 15-20 minutes before removing. Once cool enough to handle, use the parchment overhang to lift the entire brownie slab onto a cutting board. Sprinkle with flaky sea salt while still slightly warm—the salt will enhance the espresso and chocolate flavors and provide a delightful contrast to the rich sweetness. Cut into squares and serve.