Preheat your oven to 350°F (175°C). Grease a 9x13 inch baking pan or line it with parchment paper for easy removal.

In a large mixing bowl, combine the melted butter, brown sugar, and granulated sugar. Mix until well combined.

Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.

In a separate bowl, whisk together the flour, baking powder, and salt. Gradually add the dry ingredients to the wet mixture, stirring until just combined.

Fold in the chocolate chips (or nuts, if using) until evenly distributed.

Pour the batter into the prepared baking pan and spread it evenly.

Bake for 20-25 minutes, or until the top is golden brown and a toothpick inserted into the center comes out with a few moist crumbs.

Allow the blondies to cool in the pan for about 10 minutes before transferring them to a wire rack to cool completely. Cut into squares and serve.