Preheat oven to 400 degrees Fahrenheit. Lay out your pie crust in the dish (or take it out of the freezer) and poke some holes in the bottom with a fork to allow steam to escape. Place on an aluminum foil-lined cookie sheet (to catch any drippings later when the crust is filled). Bake for 10 minutes then remove from the oven and set aside. Reduce oven to 350 degrees Fahrenheit.
Combine the butter, maple syrup, and brown sugar in a medium saucepan. Heat at medium flame until the butter is melted and it just starts boiling. Try not to stir if you can--you can swirl the pan around a bit if you need to. Remove from heat and add the chopped chocolate. Set aside for 5 minutes or so, then stir in the chocolate. Let it sit for 10 more minutes.
In a mixing bowl, whip the eggs and egg yolk until frothy. Mix in the vanilla. Dribble this into the melted chocolate, stirring the entire time, until it is completely incorporated. Stir in the walnuts. Pour into your prepared pie shell and top with some un-chopped walnuts.
Bake at 350 degrees for 20 minutes. Then turn it around so the front is now facing the back of the oven. Bake for another 20-22 minutes. Allow it to cool completely before cutting.