Chop the 5 oz chocolate into roughly 1/2-inch pieces for even melting, and measure out all remaining ingredients into separate bowls. Preheat your oven to 350°F and generously grease a 10-12 inch cast iron skillet with butter or oil, making sure to coat the bottom and sides evenly—this ensures the brownies release cleanly and develop a slightly crispy edge.

Combine 14 tablespoons butter, 2 tablespoons vegetable oil, and the chopped chocolate in a medium saucepan over medium heat. Stir frequently as the mixture melts, then add 1.25 cups sugar and continue stirring until the mixture is smooth and the sugar is fully dissolved, about 5 minutes total. Remove from heat and let cool for 5 minutes—this cooling period is crucial because it prevents the eggs from scrambling when you add them. I like to use high-quality butter like Kerrygold here because it adds a subtle richness that elevates the final brownie.

Once the chocolate mixture has cooled slightly, whisk in the 3 room-temperature eggs one at a time, stirring well after each addition to fully incorporate them into the mixture. Add 2 teaspoons vanilla essence and stir until the batter is smooth and glossy. Using room-temperature eggs helps them blend seamlessly with the warm chocolate without creating clumps.

In a separate bowl, whisk together 0.5 cup cocoa powder, 1 cup flour, 0.75 teaspoon salt, and 1/4 teaspoon espresso powder. This combination of cocoa and a hint of espresso deepens the chocolate flavor without making the brownies taste like coffee—I use Ghirardelli Majestic cocoa powder specifically because it creates a richer, darker color in the final brownies.

Pour the dry ingredient mixture from Step 4 into the wet chocolate mixture from Step 3. Using a spatula or wooden spoon, gently fold the ingredients together until just combined—avoid overmixing, as this can develop too much gluten and result in tough brownies. Fold until you see just a few streaks of dry ingredients remaining, then add the 1 cup chocolate chips and fold them in gently until evenly distributed throughout the batter.

Pour the batter into the prepared cast iron skillet and smooth the top with a spatula. Sprinkle the optional 2 tablespoons chocolate chips evenly across the surface—this creates a professional, finished appearance and adds extra chocolate flavor to the top layer. Place the skillet in the preheated 350°F oven and bake for 30–36 minutes. The brownies are done when a toothpick inserted into the center comes out with just a few moist crumbs clinging to it; you want fudgy brownies, not completely set ones.

Remove the skillet from the oven and let the brownies cool in the pan for at least 5 minutes before slicing—this allows them to set enough to cut cleanly while still maintaining that fudgy interior. Serve warm from the skillet for the best texture and temperature, or let cool completely and store in an airtight container.