2Make the dough: mix flour, salt and baking powder together in a medium size mixing bowl. Cut in butter. Stir in egg, vinegar and 1/2 cup water. Continue stirring until dough is moist enough to be formed into a ball (add more water if necessary). Form the dough into a large ball.
3Make the filling: bring a pot of 3 cups water to boil, add lentils and continue to boil for 30 to 45 minutes; until lentils are tender. Watch the lentils and add water if necessary.
4Wrap the potatoes in aluminum foil and bake them for 30 minutes in the preheated oven. When the potatoes have cooled cut them into small pieces and mix them with the lentils.
5In a frying pan saute onions with oil. Stir the onions into the potato-lentil mixture; season with salt and stir.
6Divide the dough into 6 - 8-inch circles. Lay the circles on a flat, floured surface. Place one cup of filling into the center of each circle. Fold the dough around the filling; seal the edges and arrange the pasties on an ungreased cookie sheet. Bake for one hour in the preheated oven.