To make the pastry, combine the flour and salt in a large bowl. Cut in the margarine or butter with a pastry blender or 2 knives until the mixture resembles coarse crumbs. Alternately, pulse the mixture in a food processor. Stir in just enough ice water so that the mixture forms a ball and holds together. Flatten the dough into a desk, wrap in plastic wrap, and refrigerate for a least 1-hour.
Meanwhile, prepare the filling. Bring a large saucepan full of water to a boil. Add the potatoes and cook until tender, about 20 minutes. Drain and let cool. Cut the potatoes into ½-inch slices. (25 min.).
In a large skillet, heat the olive oil over medium-high heat. Add the onion and cook, stirring, for 5 minutes. Add the bell peppers, tomatoes, jalapeno, garlic, thyme, salt, and pepper. Cook over medium heat until the mixture is soft and thick, about 20 minutes. Stir in the parsley.
Preheat the oven to 375 degrees F. Divide the dough in half and roll out each piece into a 9-inch circle. Fit one round of dough into a 9-inch deep-dish pie pan or cake pan. Spread on one-third of the vegetable sauce. Top the sauce with one-third of the potato slices. Repeat layering until all the sauce and potatoes are used. Cover the pie with the second pastry circle, crimp the edges to seal, and brush the top with the egg white if desired. Bake the pie for 35 minutes, or until golden brown. Serve hot, at room temperature, or chilled.