Prepare the Blondie Batter:

1. Preheat the Oven: Preheat your oven to 350°F (175°C). Line a 9×9-inch baking pan with parchment paper or lightly grease it to prevent sticking.
2. Mix the Wet Ingredients: In a large mixing bowl, whisk together the melted butter and brown sugar until smooth. Add the eggs, one at a time, whisking well after each addition. Stir in the vanilla extract.
3. Combine the Dry Ingredients: In a separate bowl, sift together the flour, baking powder, and salt.
4. Add Dry Ingredients to Wet Ingredients: Gradually fold the dry ingredients into the wet ingredients using a spatula or wooden spoon until just combined. Be careful not to overmix.

Add the White Chocolate:

5. Stir in the White Chocolate: Gently fold in the white chocolate chips (and nuts if using) until evenly distributed throughout the batter.

Bake the Blondies:

6. Transfer to Pan: Pour the batter into the prepared baking pan and smooth the top with a spatula to ensure an even layer.
7. Bake: Bake for 30-35 minutes or until the top is golden brown, and a toothpick inserted into the center comes out clean or with a few moist crumbs.
8. Cool: Allow the blondies to cool in the pan for 10-15 minutes before transferring them to a wire rack to cool completely.

Cut and Serve:

9. Cut into Bars: Once the blondies are completely cooled, cut them into squares or bars, depending on your preferred size.