In a medium bowl, whisk together the flour, baking powder, cornstarch, and salt. In a separate bowl, stir together the butter, Nutella, and egg white. Mix in the vanilla and brown sugar, smearing any clumps along the side of the bowl. Add in the flour mixture, stirring just until incorporated. Fold in 3 tablespoons of the white chocolate chips. Cover the dough with plastic wrap, and chill for at least 2 hours.
Divide the dough into 12 pieces, and shape into balls. Flatten to about ½” in height, and press 2-3 of the remaining white chocolate chips into the tops. Bake at 350°F for 12 minutes. Cool on the pan for 10 minutes before turning out onto a wire rack.
Notes: It’s highly recommended that you chill for longer than 2 hours (i.e. closer to 4 hours) for chewier cookies.
To increase the hazelnut flavor from the Nutella, decrease the white chocolate to 2 or 3 tablespoons instead.
Recipe by Amy's Healthy Baking at https://amyshealthybaking.com/blog/2013/10/14/white-chocolate-nutella-cookies/