Preheat your oven to 350°F (175°C). Grease and flour a 9x13 inch baking pan.

In a medium saucepan over low heat, melt the unsalted butter completely. Remove it from the heat and let it cool slightly.

In a large mixing bowl, whisk together the melted butter and granulated sugar until well combined. Add in the eggs, one at a time, mixing thoroughly after each addition. Stir in the vanilla extract.

In a separate bowl, sift together the flour, cocoa powder, salt, and baking powder. Gradually add the dry mix to the wet mixture, stirring until just combined. Be careful not to overmix.

Pour the batter into your prepared baking pan and spread it evenly.

Bake in the preheated oven for about 30-35 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs.

Allow the cake to cool in the pan for at least 10 minutes before transferring it to a wire rack to cool completely.

Slice it up and serve with your favorite toppings.