Serve this potato and cheese-filled bread as a meatless appetizer or with a hearty soup for dinner.
For dough, combine warm water, yeast, and the 1 teaspoon sugar; stir to dissolve yeast. Set aside. In a large bowl mix 1-1/2 cups of the flour, 2 tablespoons sugar, and the 1/2 teaspoon salt. Make a well in the center; stir in egg. Heat milk to 120 degree F to 130 degree F; stir into flour mixture. Stir in 2 tablespoons melted margarine and the oil. Stir in yeast mixture. Using a spoon, stir in as much of the remaining flour as you can.
Turn out onto a floured surface. Knead in enough remaining flour to make a moderately stiff dough that is smooth and elastic (6 to 8 minutes total). Shape into a ball. Place in a greased bowl; turn dough once. Cover; let rise in a warm place until double (about 1 hour).
Meanwhile, for filling, place potatoes in a medium saucepan; add water to cover. Sprinkle with a little salt. Bring to boiling. Reduce heat and simmer, covered, for 20 to 25 minutes or until tender; drain. Add cheddar cheese, 2 tablespoons margarine or butter, and the 1/4 teaspoon salt; mash until smooth. Set aside.
Punch dough down. Turn out onto a lightly floured surface. Divide dough in half. Cover and let rest 10 minutes. On a lightly floured surface, roll one portion of dough into a 15x12-inch rectangle. Transfer rectangle to a lightly greased baking sheet. Spread filling over dough to within 1 inch of edges. Roll remaining dough to a 15x12-inch rectangle; place over filling. Pinch edges to seal. Prick dough every 2 inches to allow steam to escape.
Bake in a 400 degree F oven about 20 minutes or until golden brown, covering with foil the last 5 minutes. Brush with 1 tablespoon melted margarine. Serve warm or cool. Makes 24 to 30 appetizer servings.