Preheat your oven to 350°F (175°C).
Line a 9x13-inch baking pan with parchment paper. (Pro tip: leave a little overhang on the sides it makes lifting the brownies out a breeze.) Lightly grease the parchment too, just to be safe.
In a medium saucepan, melt the butter over medium heat. Once it’s fully melted, take it off the heat and stir in the sugar. It’ll look kind of gritty that’s okay.
Add the eggs, one at a time, whisking well after each. Stir in the vanilla.
In a separate bowl, whisk together the flour, cocoa powder, baking powder, and salt.
Slowly add the dry ingredients to the butter mixture, stirring until everything is just combined.
Pour the batter into your prepared pan, spread it out evenly, and pop it into the oven.
Bake for 25–30 minutes, until a toothpick poked into the center comes out with a few moist crumbs.
Let the cake cool completely in the pan on a wire rack don’t rush this part, or your frosting will melt right off.