Peruvian purple potatoes are rich in the antioxidant anthocyanin. Their nutty taste and beautiful appearance set them apart from other potatoes. This recipe is just one of many great ways to use these medium-starch potatoes.
Preheat the oven to 400 degrees.
Place the potatoes in a pot, cover with cold water, and season with salt, to taste. Bring to a boil and blanch for 2 minutes. Drain, and cool. In a large sauté pan, heat the olive oil, add the onions and garlic and season with salt and pepper, to taste. Sauté the onions until caramelized, about 8-10 minutes. Add the butter and melt. Make layers with the sliced potatoes and onions, and let cool.
Lightly dust a work surface with flour. Unfold the puff pastry sheet and roll into a 14-inch square. Cut into four 7-inch squares. Brush the edges of the pastry squares with the egg mixture. Fold the corners of the pastry squares toward the center over the potato and press to seal. Repeat with the other sheet.
Place the filled pastries seam side down onto a baking sheet. Brush the pastries with the egg mixture. Bake until the pastries are golden brown, about 25 minutes. Let the pastries cool on the baking sheet for 10 minutes.