Preheat your oven to 325 degrees Fahrenheit.
Butter an 8-inch square baking dish using 1 teaspoon of butter.
Cut a piece of parchment paper to line the bottom and two sides of your prepared dish.
In a medium bowl, mix the sugar, melted butter, eggs, and vanilla extract until well combined.
Use a spoon or whisk to ensure these ingredients are thoroughly blended.
Combine the unsweetened cocoa powder, all-purpose flour, salt, and baking powder in a separate bowl.
Gradually add this dry mixture to the wet ingredients, stirring until just combined.
Gently fold in the chopped nuts if you're using them.
Spread the batter evenly into the prepared baking dish, smoothing the top with a spatula.
Bake the brownies in the preheated oven for about 20-25 minutes.
Ensure a toothpick inserted into the center comes out with a few moist crumbs before removing.