Preheat your oven to 350°F (175°C).

Grease your 9x13 inch baking pan with butter or line it with parchment paper.

In a mixing bowl, combine the melted butter and sugar, whisk until smooth, then add the eggs and vanilla, mixing until fully incorporated.

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

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

Transfer the brownie batter to the prepared baking pan, spreading it evenly.

Bake in the preheated oven for about 30 minutes.

Remove the brownies from the oven and let them cool in the pan for about 10 minutes.

Use a sharp knife to cut them into squares.