For the dough, I use the food processor: place all the ingredients together, set the food processor to maximum speed and mix till you get a "ball". Place dough in the refrigerator. Finely chop the onions and place them in a large pan with half of the butter for the filling. Cover and simmer until onions are dissolved. Add the remaining butter; when it's melted, add the flour, stirring in well. When the flour is dissolved, take the pan off the heat and pour the milk, all together. Mix well, then place the pan back on the fire and cook until it starts boiling. Now, add cheese, egg and seasonings. Pat dough evenly on bottom and 1 inch around sides of 12-inch baking dish. Pour in the filling and bake at 400 for 30 to 45 minutes, until golden brown.