Preheat oven to 350°F.
Line baking sheet with parchment paper.
Beat butter and sugars creamy.
Add egg, yolk, vanilla, baking soda, and salt.
On low, add flour.
Stir in Kit Kats and chocolate chips.
Drizzle on the melted chocolate and just give it a few stirs so it looks like ribboned chocolate.
Scoop large mounds onto cookie sheet.
Press on a few of the extra kitkats and bake 9-11 mins.
Cool on sheet.