• 10 Tablespoons unsalted butter cut into pieces (141g) • 6 oz premium white chocolate bar like Ghirardelli or Lindt, chopped (170g) • 1 ¼ cups granulated sugar (250g) • 2 large eggs + 1 large egg yolk • ½ teaspoon vanilla extract • 1 ¾ cups all-purpose flour (220g) • 1 teaspoon salt • ¼ teaspoon baking powder • 1 cup white chocolate chips (170g)

Combine butter and chopped white chocolate pieces in a microwave safe bowl. Heat in  20-second increments, stirring in between, until melted and smooth.

In a separate bowl, combine sugar, eggs, and egg yolk and whisk vigorously until pale yellow (about 30 seconds).

Stir in vanilla extract then add chocolate mixture and stir until completely combined.

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

Stir into white chocolate mixture until thoroughly combined.

Use a spatula to fold in chocolate chips and spread evenly into prepared baking pan.

Transfer to center rack of 325F (165C) oven and bake for 42 minutes or until a toothpick inserted in the center comes out clean or with moist crumbs.

Allow to cool before slicing and serving.