Preheat your oven to 325°F and grease a 9x13 inch baking pan (or 8x8 for thicker brownies). While the oven heats, sift together the flour, cornstarch, baking powder, salt, and cinnamon in a medium bowl. Sifting removes any clumps and incorporates air, which helps create a more tender crumb. Set this dry mixture aside—you'll fold it in at the end to avoid overdeveloping gluten.

Combine the milk and apple cider vinegar in a small bowl and let sit for 5-8 minutes—this creates a buttermilk-like substitute that mimics the binding and moisture of eggs. While it's resting, melt the butter in a medium saucepan over medium heat, then continue cooking it for 3-5 minutes, swirling occasionally, until it turns golden brown and develops a nutty aroma. I use Kerrygold butter because its higher fat content browns beautifully and adds incredible depth to the brownies. Once browned, remove from heat and let cool slightly while you proceed.

Add the packed brown sugar and sugar to the cooled brown butter, stirring constantly for 2-3 minutes until the sugars partially dissolve and the mixture becomes thick and glossy. This time and friction helps dissolve the sugar and creates a smooth batter. Pour in the milk mixture from Step 2 and microwave the entire mixture for about 2 minutes—this gentle heat helps fully dissolve the sugar and creates the right consistency for binding the dry ingredients later.

Whisk the warm wet mixture vigorously for 1-2 minutes until the sugar is completely dissolved and the batter looks smooth. Add the cocoa powder, vanilla essence, and espresso powder, stirring constantly for another 2 minutes until the cocoa is fully incorporated and no lumps remain. The espresso powder deepens the chocolate flavor without adding coffee taste—I always include it for rich, complex brownies. At this point, your batter should be silky and dark brown.

Gently fold the dry ingredient mixture from Step 1 into the chocolate batter using a rubber spatula, stirring until just combined—avoid overmixing, which would toughen the brownies. Fold in the chocolate chips, then pour the batter evenly into your prepared pan, using the spatula to smooth the top.

Bake at 325°F for 40-50 minutes, until a toothpick inserted into the center comes out with just a few moist crumbs—don't overbake or the brownies will be dry. Remove from the oven and let cool completely in the pan before cutting into squares. I find that cooling in the pan helps the brownies set properly and keeps them fudgy inside.