Preheat the oven to 375 degrees Fahrenheit. Line a baking sheet with Gefen Parchment Paper and set aside.

In a mixing bowl, combine the flour and salt.

Add the cold, cubed margarine and blend until the mixture resembles coarse, damp sand.

Stir in the egg yolk, ice-cold water, and vinegar.

Mix just until a sticky dough forms.

Refrigerate for at least one hour or overnight for best results.

Boil the peeled Yukon potatoes in salted water until fork-tender. Drain and allow to cool.

Meanwhile, heat two tablespoons of oil in a pan and sauté the diced onion until golden brown.

Let the onions cool completely.

In a large bowl, mash the cooled potatoes using a potato masher, leaving small chunks for texture.

Add the eggs, 1/4 cup oil, kosher salt, and black pepper.

Mix until well combined, then gently fold in the sautéed onions.

Lightly flour a work surface and divide the chilled dough into 12 equal portions.

Roll each portion into a ball and flatten into a circle.

Place a scoop of the potato filling in the center of each circle, fold over, and shape into a ball, sealing the edges.

Arrange the filled buns seam-side down on a parchment-lined baking sheet.

For a golden finish, brush each bun with beaten egg and score the tops with a sharp knife to allow steam to escape.

Bake for 40 minutes or until the tops are lightly golden and the pastry is crisp.

Take a bite and enjoy!