Preheat your oven to 350°F (175°C) and grease a 9×13-inch baking pan or line it with parchment paper.

In a medium saucepan, melt the unsalted butter over low heat. Once melted, remove from heat and let it cool slightly.

In a large mixing bowl, combine the melted butter and granulated sugar. Stir until well combined. Then, add in the eggs one at a time, mixing thoroughly after each addition, followed by the vanilla extract.

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

Gradually add the dry ingredients to the wet mixture, stirring until just combined. Be careful not to overmix; a few lumps are okay.

Gently fold in the chocolate chips and your choice of candy pieces, making sure they are evenly distributed.

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

Place the pan in the preheated oven and bake for about 25-30 minutes or until a toothpick inserted into the center comes out with a few moist crumbs.

Allow the brownies to cool in the pan for at least 10 minutes before cutting them into squares. Serve warm or at room temperature.