Preheat oven to 350°F. Spray an 8X8 pan with baking non-stick spray. Line the bottom and 2 sides of the pan with parchment paper. Spray again.
Melt the butter in the microwave, let it slightly cool. In a mixing bowl, mix the butter, brown sugar, and vanilla together. Mix in eggs and egg yolk.
3/4 cup Unsalted butter, 1 1/2 cups Brown sugar, 2 Large eggs, 1 tsp Pure vanilla extract, 1 Egg yolk
Pour in flour and salt. Mix until combined. Add in white chocolate chips.
2 cups All-purpose flour, 1/2 tsp Salt, 3/4 cup White chocolate chips
Pour batter into the pan. Bake for 30-40 minutes. They are done baking when the blondies are set with no more jiggle.
Cool the blondies completely.