To make filling, peel the potatoes, cut them into chunks, boil in salty water until tender. Use a fork to test, not a knife, it is not accurate. Drain well, mash or use a ricer to make a smooth puree. Stir in salt, not too much, you salted the water already and pepper. Fry your onions in a couple of tablespoons of oil until medium brown.You can do this way before hand and keep refrigerated. Add browned onions to your potatoes, adjust seasonings, if you like at this time you can add a little garlic powder or chives, it's all good. I like mine a little peppery. Cover tightly and refrigerate until chilled.
To make the dough, put 3 cups flour in the middle of a clean counter and mix in baking powder, no need for a bowl. Make a nice deep well in the center. In a bowl combine oil, eggs, salt, pepper. Pour into center of flour and using your fingers (less dishes!)start incorporating your wet into the dry. When you get a rough ball scrape the counter with a knife or a spatula to get all of what's left on the counter. Put aside. Using some of the 1/2 cup flour you have left over, knead dough for a minute or two until you have a slightly sticky dough. Wrapped in plastic wrap and refrigerate for an hour.
When your filling has cooled and your dough has rested in the refrigerator for an hour. Cut the dough into 4 equal pieces. Roll out on slightly flour surface to an 18" X 8" rectangle. Place the dough with long side facing you. Start placing your filling, 2 inches above the bottom of the dough lay out a 2 inch wide roll of the filling. Take the botton two inches of dough and fold over the filling. Taking your prepared egg wash brush the upper edge, about an inch or two wide. This in not science. With the palms of your hands,rolled the filled portion over the egg wash portion.Grease 2 baking sheets. Carefully place on baking sheet, you may want to have some help. Four hands are better than two, plus it will get your husband to maybe stand up. Repeat with the other 3 portions of dough. Place in a preheated 375 F. oven. Bake until golden brown, about 50 minutes.
To serve, cut the rolls into crosswise pieces about 2 inches wide.