Step 1: Prepare the Oven: Preheat the oven to 350°F (175°C). Lightly grease an 8x8-inch baking pan or line it with parchment paper for easy removal.

Step 2: Combine Butter and Sugar: In a large mixing bowl, whisk together the melted butter and sugar until smooth and glossy.

Step 3: Add Eggs and Vanilla: Add the eggs one at a time, whisking well after each addition. Stir in the vanilla extract until fully combined.

Step 4: Mix Dry Ingredients: In a separate bowl, sift together the Hershey's cocoa powder, flour, baking powder, and salt.

Step 5: Make the Batter: Gradually add the dry ingredients to the wet ingredients. Fold gently using a spatula until just combined. Do not overmix.

Step 6: Add Optional Mix-Ins Fold in chocolate chips and nuts if using.

Step 7: Transfer to Pan : Spread the batter evenly into the prepared baking pan.

Step 8: Bake: Bake for 28 to 32 minutes, or until a toothpick inserted near the center comes out with a few moist crumbs attached.

Step 9: Cool Allow the brownies to cool completely in the pan for at least 30 minutes before slicing.

Step 10: Serve: Cut into 16 squares and serve. Enjoy as-is or with vanilla ice cream for an extra indulgent dessert.