Roast the garlic at 375F for 1 hr or until golden. Let it cool.
Blend the garlic with the milk. Add the cream, milk, warm up.
Using a mandoline, thinly slice the potatoes.
Rub butter on a baking dish (using an 8x8) and place 2 sheets of parchment paper overlapping each other.
Add a ladleful of the cream, arrange a layer of potatoes, more cream and more potatoes. Add a VERY thin layer of cheese followed by a layer of potatoes, cream, potatoes, more cheese, potatoes, cream, potatoes, cream, cheese, potatoes, cream, potatoes & cream. A total of 8 layers of potatoes.
Cover with foil. Bake at 350F for 75 min.
Let cool. Place parchment paper over the potatoes, a baking sheet on top and heavy cans. Refrigerate for 8 hours minimum. I do overnight.
Slice off the edges. Cut into stacks.
Place on a baking sheet lined with parchment paper, top with the rest of the gruyere and parm.
Bake at 425F for 35-45 min until deeply golden. Top with chives and serve.