Step 1: Preheat and Prepare Pan
Preheat oven to 350°F (175°C). Line an 8×8-inch square baking pan with parchment paper, leaving overhang on two sides for easy removal. Lightly grease the parchment with butter or cooking spray. Set aside.

Step 2: Melt Butter and Chocolate
In a medium saucepan over low heat, melt butter and chopped chocolate together, stirring constantly until completely smooth and melted. Remove from heat and let cool for 3-5 minutes. (Alternatively, melt in microwave in 30-second intervals, stirring between each.) Pour melted mixture into your large mixing bowl.

Step 3: Add Sugar
Add granulated sugar to the chocolate-butter mixture in the bowl. Whisk vigorously for about 30-45 seconds until well combined and smooth. The mixture should look glossy and slightly thickened.

Step 4: Add Eggs and Vanilla
Add eggs one at a time, whisking well after each addition. The mixture should become thick, smooth, and lighter in color. Add vanilla extract and whisk until fully incorporated. This vigorous whisking incorporates air and helps create that beautiful crackly top!

Step 5: Add Dry Ingredients
Add flour, cocoa powder, salt, and espresso powder (if using) directly to the wet ingredients in the same bowl. Using a rubber spatula or wooden spoon (switch from whisk now), fold and stir gently just until no dry streaks remain. Don’t overmix! The batter should be thick, smooth, and glossy. If using chocolate chips, fold them in now.

Step 6: Pour and Bake
Pour batter into prepared pan, spreading evenly with spatula to reach all corners. Tap the pan gently on the counter 2-3 times to release air bubbles. Bake for 25-30 minutes. Brownies are done when edges look set and center has just a slight jiggle. A toothpick inserted 2 inches from edge should come out with moist crumbs – not wet batter, but not completely clean. Don’t overbake!

Step 7: Cool
Remove from oven and let cool in the pan on a wire rack for at least 20-30 minutes. The brownies will continue to set as they cool. For cleanest cuts, cool completely (about 1 hour) before cutting.

Step 8: Cut and Serve
Use the parchment overhang to lift brownies out of pan. Place on cutting board and cut into 16 squares with a sharp knife, wiping blade clean between cuts. Serve and enjoy!