Step 1: Preheat and Prepare
Preheat oven to 350°F (175°C). Line an 8×8-inch or 9×9-inch square baking pan with parchment paper, leaving overhang on two sides for easy removal. Alternatively, grease the pan generously with butter or cooking spray. Set aside.

Step 2: Mix Wet Ingredients
In a large mixing bowl, whisk together the Greek yogurt, sugar, melted butter (or oil), eggs, and vanilla extract until smooth and well combined. The mixture should be creamy and uniform with no lumps of yogurt visible. Whisk vigorously for about 30 seconds to incorporate some air.

Step 3: Combine Dry Ingredients
In a separate medium bowl, whisk together the flour, cocoa powder, baking powder, and salt. Whisk thoroughly to break up any lumps in the cocoa powder and ensure even distribution. If you have a sifter, you can sift the cocoa powder first for extra smoothness, though this isn’t strictly necessary.

Step 4: Combine Wet and Dry
Add the dry ingredients to the wet ingredients. Using a rubber spatula or wooden spoon, gently fold the mixture together until just combined. Don’t overmix – stir just until no dry flour streaks remain. A few small lumps are fine! Overmixing develops gluten and creates cakey, tough brownies instead of fudgy ones. The batter will be thick and somewhat glossy.

Step 5: Add Mix-Ins (Optional)
If using chocolate chips, gently fold them into the batter, reserving a small handful to sprinkle on top if desired.

Step 6: Bake
Pour the batter into your prepared pan, spreading it evenly with a spatula to reach all corners. If you reserved chocolate chips, sprinkle them over the top now. Bake for 25-30 minutes. Start checking at 23 minutes – the brownies are done when a toothpick inserted in the center comes out with a few moist crumbs (NOT wet batter, but definitely not clean). The edges should look set and possibly start pulling away from the pan slightly, while the center should still look slightly soft. Remember, brownies continue cooking from residual heat, so slightly underbaked is better than overbaked!

Step 7: Cool Completely
Remove from oven and place the pan on a wire cooling rack. Let the brownies cool in the pan for at least 15 minutes, then use the parchment overhang to lift them out onto the cooling rack. Let cool completely before cutting – this takes patience but ensures clean cuts and proper texture! At least 1 hour of cooling is ideal.

Step 8: Cut and Serve
Once completely cool, cut into 16 squares using a sharp knife. For the cleanest cuts, wipe the knife between each cut. Serve and enjoy! These are delicious on their own or with a glass of cold milk.