Start by preheating your oven to 350°F (175°C). Line a 9x9-inch baking pan with parchment paper, letting the edges hang slightly over the sides—this makes removal and slicing so much easier. Lightly spray the parchment with non-stick baking spray. Why this matters: parchment prevents sticking while maintaining the brownie's edges, and the slight overhang means you can lift the entire slab out whole. Set your pan aside.

In a large mixing bowl, sift together the all-purpose flour, baking powder, fine salt, unsweetened cocoa powder, and espresso powder if you're using it. Sift this mixture—don't just stir it. Sifting aerates the cocoa and removes lumps, which ensures smooth, even chocolate distribution throughout your brownies. This is one of those steps that feels fussy but makes a real difference. Set this bowl aside—you'll need it in just a moment.

In a medium saucepan, combine the unsalted butter, neutral oil, and ⅓ cup of the granulated sugar. Place this over medium heat and stir frequently until the butter melts completely and the mixture is smooth. This should take about 3-4 minutes. Don't let it bubble or get too hot—you want it warm enough to create steam, but not so hot it will cook your eggs when you add them. Remove from heat immediately once the butter is melted and the sugar slightly dissolves.

In another large mixing bowl, combine your two room-temperature eggs, one egg yolk, the remaining 1 cup of sugar, and pure vanilla extract. Using a whisk, beat this mixture for about 30 seconds until it's well combined and slightly pale. You're not trying to whip air into it like you would for a cake—just combine everything thoroughly. This is a key moment: room temperature eggs whisk smoothly and incorporate the warm butter mixture without curdling.

Now comes the moment that determines your success: slowly pouring the warm butter mixture into the egg mixture while whisking constantly. This is not a step to rush. Pour just a tiny bit—maybe a tablespoon—of the warm butter into your eggs while whisking vigorously. Once that's combined, add another small splash and whisk again. Keep going, adding the butter gradually in small amounts and whisking constantly, until it's fully incorporated. This slow combination creates a stable emulsion that gives you that signature fudgy texture. If you dump it all in at once, you'll either scramble the eggs or create a broken, separated batter.

Once your butter and egg mixture is completely combined and smooth, add your sifted dry ingredients and chocolate chips to the bowl. Using a rubber spatula, slowly stir until just combined. This is critical: stop the moment you see the last trace of dry flour disappear. Do not keep stirring. Do not make extra passes with your spatula. Overmixing develops gluten, which turns your brownies from fudgy to cakey. I know it's tempting to make sure everything is perfectly blended, but resist that urge. A few faint streaks of flour are infinitely better than overmixed batter.

Scrape every bit of batter into your prepared 9x9-inch pan. Using the same rubber spatula or an offset spatula, gently smooth the top. Don't press down hard—let the batter settle naturally. You want an even surface, but you're not compacting the batter.

Place the pan in your preheated 350°F oven. Bake for 28 to 30 minutes. You're looking for specific visual cues here: the edges should be firm and pulling away slightly from the pan, and the top should be shiny with a thin, slightly cracked surface. A toothpick inserted into the center should come out with just a few fudgy crumbs—not clean, and not wet. If you pull it out and it's completely clean, you've overbaked it.

Remove the brownies from the oven and place the pan on a cooling rack. Do not skip the cooling step. Brownies continue cooking slightly from residual heat, and they set up properly as they cool. Let them cool completely at room temperature—this takes about 2 hours. Resist every urge to cut into them early. I know the chocolate smell is incredible, but warm brownies fall apart. Once they're completely cool, you can cut them into nine perfect 3x3-inch squares. A sharp knife dipped in hot water and wiped dry between cuts helps you get clean edges.