Preheat the oven to 350°F (175°C).

Grease the 9-inch round cake pan or line it with parchment paper.

In a mixing bowl, whisk together the granulated sugar and melted butter until well combined.

Beat in the eggs one at a time, followed by the vanilla extract.

In a separate bowl, whisk together the flour, cocoa powder, salt, and baking powder.

Gradually add the dry mixture into the wet ingredients, stirring until just combined.

Pour the batter into the prepared cake pan, smoothing the top with a spatula.

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