Preheat your oven to 350°F and line a 13" x 9" baking pan with parchment paper. Leave some hang over the edges for easy removal; set aside.
In a medium bowl, combine the flour, baking powder, and salt. Set aside.
In a large mixing bowl, whisk together the melted butter, brown sugar, and white sugar until well combined. You can use a hand mixer if you would like. I prefer to use a whisk as this is an easy recipe to whip up.
Add the vanilla extract and the eggs, whisk until fully incorporated.
Add the flour mixture into the wet batter and mix until just combined. Fold in the white chocolate and the sprinkles.
Pour the batter (it will be thick) into your prepared baking pan. Spread batter evenly and top with more sprinkles. You may need to lightly spray your hands with non stick spray to help spread the batter evenly as it is thick.
Bake for 25-30 minutes, or until the top is set and lightly brown. Remove from oven and cool completely before cutting. Blondies will keep in an airtight container for up to 3 days, or refrigerated for up to a week.