Really Crispy Potatoes

REALLY CRISPY POTATOES
(We watched this on America's Test Kitchen, and I didn't get the name of this recipe, so the name above is my description of the potatoes.)
2.5 pounds Yukon Gold Potatoes
5 tablespoons unsalted butter, divided
1 teaspoon salt
1/2 teaspoon black pepper
1 1/2 teaspoons Rosemary (I didn't have Rosemary, so I used parsley)
1 teaspoon corn starch
     Wash the potatoes.  (I peel mine but you can leave the peelings on.)  Cut into 1/8-inch slices.  Place into a large bowl of cold water to remove the starch.  Swish around with your hands, then drain the potatoes in a colander.  Dry the sliced potatoes really well by dumping some onto a clean kitchen towel and drying with another clean kitchen towel.  Let sit as you prepare the flavoring. (At this time I turned the oven to 450 degrees to heat it up.)
     To flavor the potatoes prepare the following in a bowl that will hold the potatoes.  (I just rinsed out the bowl that I had used and dried.)  Melt 4 tablespoons unsalted butter, whisk in the salt, pepper, rosemary and corn starch.  Add the potatoes to the bowl and, using the best two tools in the kitchen--your hands--toss the potatoes with the butter mixture until well coated.
     Prepare the pan--they used a 10-inch non-stick frying pan that the handle could be put in a hot oven.  I used my castiron frying pan--the heavier one.  Put 1 tablespoon melted butter into the pan and coat all the sides and the bottom (you may have to use your fingers).  Arrange a layer of potatoes on the bottom (starting at the center and moving out to the edges), this is for appearance.  Then dump in the rest of the potatoes and move around and press down until it feels level.  Place the skillet on the stovetop and turn the heat to medium high, and cook about 5 minutes--just to sizzling.
     Place a square of sprayed aluminum foil over the potatoes, pressing it down.  Put a 10-inch round cake pan on the foil, and place pie weights in the cake pan.  (This is to weigh down the potatoes.)  Place in a 450 degree oven and bake 20 minutes.  Remove the cake pan and foil from off the potatoes, and continue baking another 20 minutes. 
     America's Test Kitchen, then removed the pan of potatoes from the oven and placed on the stove top and over medium heat, shook the frying pan until the potatoes loosened from the bottom of the pan--this only took a minute or two.  (This did not work with the castiron skillet.)  Invert the potatoes onto a serving platter, slice and serve.
     This potatoes are really crispy on the outside and fluffy on the inside.  The taste is really good, too.  I can't wait until our Yukon Gold potatoes are ready.  We have just been using Russet, Burbank.  To do in a 12-inch Dutch Oven, we put aluminum foil in the bottom and sides; followed the directions above adjusting the potatoes and flavoring as needed for the number of potatotes we used, put 10 briquets on the bottom and loaded the top.  We put the sprayed foil over the potatoes, and weighted it down with a 10-inch Dutch Oven lid, baked 25 minutes.  Removed the 10-inch lid and foil and continued baking another 25 minutes.  The potatoes didn't get very crispy, but they were very delicious.