Place potatoes in a large pot and pour in water to cover by 2”; season with salt. Bring to a boil over medium-high heat. Reduce heat and simmer until a paring knife very easily slides through potatoes, 25-36 minutes. Drain and let cool slightly.
Preheat the oven to 425 degrees F. Whisk egg yolks, garlic, cream, sour cream, butter, and peppercorns in a large bowl. Season generously with salt.
Peal Potatoes.
Pass peeled potatoes through a ricer or a food mill (or mash them by hand if you don’t mind a few lumps).
Shred them right into the bowl with the egg mixture. Fold in gently being careful not to overmix. Transfer to a 3 quart baking dish and decoratively shingle or swirl the surface. Bake, rotating once, until golden brown and slightly puffed, 30 or 40 minutes.