9 large russet potatoes
3/4 c butter
1 T garlic
1/2 c milk
3-1/2 oz grated parmesan
5-1/2 t salt
1/1 t pepper
6 egg yolks
2 T olive oil
Preheat oven to 425. Place forked potatoes directly on oven rack and bake until fork tender (about 1 hour). Remove from oven and let stand until cool enough to handle but still hot (about 15 minutes).
While potatoes cool, melt butter over medium heat. Add garlic and cook until dissolved. Stir in milk and cook until just warm (about 30 seconds). Remove from heat but keep warm.
Cut potatoes in half lengthwise. Scoop out cooked potatoes into a large bowl, leaving about 1/8-inch flesh in the skin. Reserve 12 skins, discard the rest (or use for potato skin appetizers).
Whisk or mash potatoes until smooth with no lumps (1-2 minutes). Stir milk mixture, cheese, salt and pepper into potatoes. Using a whisk, beat egg yolks vigorously into potato mixture one at a time, scraping bowl sides as needed.
Brush outsides of potato skins with olive oil; place on a large rimmed baking sheet. Working in batches, transfer potato mixture into a pastry bag with a large star tip and pipe into skins in decorative patterns.
Bake at 425 until browned on top, about 25 minutes. Garnish with pepper, parsley and sea salt.