Preheat your oven to 350°F and grease a 9x13 inch baking pan with butter or cooking spray. While the oven preheats, sift together the flour, salt, cocoa powder, and ground cinnamon in a medium bowl to remove any lumps and ensure even distribution of the cocoa and spices. Set this dry mixture aside—sifting now prevents lumps from forming later when you fold it into the wet ingredients, which would create dense pockets in your brownies.

Combine the melted butter, dark chocolate chips, and espresso powder in a microwave-safe bowl. Heat in 30-second intervals, stirring between each interval, until the chocolate is completely smooth and melted—typically 1-2 minutes total depending on your microwave. I find that espresso powder dissolves best when whisked directly into warm melted chocolate rather than added later, and this gives you a deeper, more integrated coffee flavor that enhances the chocolate without making it taste overtly like coffee. Let the mixture cool to room temperature before proceeding to the next step.

Add the sugar, room-temperature eggs, and vanilla to the cooled chocolate mixture and stir vigorously for about one minute until the mixture is well combined and slightly lighter in texture. The room-temperature eggs are important here—they incorporate more smoothly and create a better emulsion with the chocolate, resulting in a richer, more fudgy texture. Using cold eggs from the refrigerator can cause the batter to seize or become grainy.

Add the dry ingredient mixture from Step 1 to the wet ingredients and stir just until combined—don't overmix, as this can develop too much gluten and make the brownies tough rather than fudgy. Fold in both types of chocolate chips (the dark and semi-sweet). I like to reserve a small handful of chips to sprinkle on top before baking for extra chocolate texture on the surface, but this is optional.

Pour the batter into your prepared pan and spread it evenly. Bake at 350°F for 28-30 minutes—the brownies are done when a toothpick inserted into the center comes out with just a few moist crumbs clinging to it (not completely clean, as you want them fudgy, not cake-like). The baking time may vary slightly depending on your oven, so start checking at 25 minutes. Remove from the oven and let cool in the pan for at least 15 minutes before cutting.

Once the brownies have cooled slightly in the pan, cut them into squares of your desired size. For the cleanest cuts, use a sharp knife and wipe it clean between each cut. You can serve them warm with a scoop of vanilla ice cream, or let them cool completely to room temperature for a denser, more fudgy texture. Store leftovers in an airtight container at room temperature for up to 5 days.