Step 1Bring a pot of water to a boil and place potatoes to cook until just tender, 10 to 15 minutes. Remove the potatoes using a skimmer and place in a large bowl. Continue to heat the pot of water. Season with 1/2 teaspoon salt and 1/8 teaspoon pepper, or to taste, and drizzle with 1 teaspoon each vinegar and oil, or as desired.
Step 2In a skillet heated over medium-high heat until hot, add a little oil and the onions. Sauté the onions until softened, 5 to 7 minutes. Remove from heat and add to the potatoes.
Step 3Plunge the greens into the pot of boiling water quickly to wilt, about 60 seconds (this may need to be done in batches). Remove and, when cool enough to handle, squeeze the excess water from the greens. Finely chop the greens and add to the potato and onion mixture. Adjust the seasoning with 1/2 teaspoon salt, 1/8 teaspoon pepper, 2 tablespoons olive oil and 3 to 4 tablespoons vinegar, or to taste.
Step 1In a large bowl, combine the flour, 1 cup water, the oil and salt, and knead until a smooth dough is formed, adding a little water if the dough feels a bit dry or a little flour if the dough feels too wet and sticky. Divide the dough into 10 equal pieces, rolling them into spheres and covering them so they do not dry out.
Step 2On a lightly floured surface, roll each piece of dough into a 6-inch round. Place about ½ cup filling on one round, and brush the outer edge with a very thin coating of water. Cover the filling with a second round, pinching the seams together and proceed until all of the flatbreads are stuffed.
Step 3Heat a cast iron griddle over medium-high heat until hot.
Step 4Heat 1 tablespoon grapeseed oil and cook the flatbreads on each side until golden brown, 3 to 5 minutes. Sprinkle the tops with flaked salt and cover with a towel to keep warm while you cook the remaining flatbreads.
Step 5Cut the flatbreads into wedges before serving.