Preheat oven to 325 degrees F.

In a medium bowl melt butter in microwave. Whisk in white and brown sugar until completely dissolved. Whisk in egg and egg yolk. Stir in vanilla and set aside.

In a large bowl combine flour, baking soda, cornstarch, and salt. Pour butter-sugar-egg mixture over flour mixture, and gently stir until dough forms. Fold in hazelnuts and chocolate chips. If dough is too sticky refrigerate for 15-30 minutes.

Using your hands, roll dough into 12-16 ¼ cup dough balls. Flatten and insert truffle. Wrap dough around truffle and roll in hands to seal dough. Arrange on cookie sheet 4 inches apart. Bake until just set, about 15 minutes. Let cool on cookie sheet for 10 minutes, then cool completely on a wire rack.

Once cookies are cool, melt chocolate until it’s thin enough to drizzle, about 1 minute in the microwave on 50% power. Drizzle, use a frosting bag, or just spread chocolate on cookies. Sprinkle with hazelnuts and enjoy!