Preheat your oven to 350°F and grease an 8x8-inch baking pan. I line mine with parchment paper too, which makes it so easy to lift the whole pan of brownies out after baking. Tap the paper down in the corners so it doesn't slide around while you're mixing.

Melt the butter in a microwave-safe bowl for about 60 seconds, stirring halfway through. Once it's melted, add the granulated sugar and stir until combined—it'll look kinda gritty and that's exactly what you want. This is where you'll add both eggs and whisk them in really well.

Pour in the alcohol-free vanilla extract and milk, then whisk everything together until smooth. The mixture should look shiny and slightly thick at this point. Don't skip the milk because it keeps the brownies from getting too dense.

In a separate small bowl, whisk together the unsweetened cocoa powder, all-purpose flour, baking powder, salt, and espresso powder. Make sure there aren't any cocoa lumps hiding in there—break them up with your whisk as you go. This prevents weird grainy spots in your finished brownies.

Add the dry ingredients to your wet mixture and fold together gently with a spatula until just combined. You want to see a few streaks of flour disappear, but don't overmix it—that's how you get tough brownies instead of fudgy ones. Fold in the chocolate chips and walnuts last.

Pour the batter into your prepared pan and spread it in an even layer. The batter will be thick and that's perfect—use a spatula to smooth the top. Mine always sticks a little to the spatula and that's completely fine.

Bake for 28-32 minutes until a toothpick inserted in the center comes out with just a few moist crumbs clinging to it. Don't pull them out when the toothpick comes out clean, or you'll get cakey brownies instead of fudgy ones. Let them cool in the pan for 15 minutes, then transfer to a wire rack.