Preheat your oven to 350°F and grease a 9×9 inch baking pan.
In a small saucepan, melt the butter over low heat.
Remove the pan from the heat and stir in the sugar, eggs, and vanilla until well combined.
Add the cocoa powder, flour, salt, and baking powder, and stir until smooth.
Fold in the rainbow chocolate chips until evenly distributed.
Pour the batter into the prepared baking pan and spread it out evenly.
Bake for 20-25 minutes, or until a toothpick inserted into the centre comes out clean.
Allow the brownies to cool completely before cutting into squares.