Preheat oven to 350F.

In a large skillet, fry the bacon till crisped. Drain on paper towels. In the same pan, saute the onions in the bacon fat till golden brown. Drain on paper towels.

Pour the bacon fat out of the pan, then place on medium heat. Add beef, salt and pepper, then cook and stir till meat is browned through. Stir in the potato flakes and egg: set aside.

For the Topping, melt the 1/4 cup butter in a small saucepan. Stir in 1/4 cup potato flakes; set aside.

For the Crust, in a medium bowl, combine the flour, sugar, baking powder and baking soda and remaining potato flakes. Cut in the 1/2 cup butter; add milk and mayonnaise. Blend until a soft dough forms. If dough is too dry, add the extra 2 tablespoons of milk.

Divide the dough in half. On a floured surface, roll one portion of dough into a 10-in. circle. Place on an ungreased cookie sheet.

Mound the browned beef on top, spreading to within 1 inch of the edge. Beginning with the onions, layer the onions, bacon, ketchup, relish and mustard on top of the beef. Add the shredded cheese last.

Roll out the remaining dough and place on top of the filling. Seal and flute edges.

At this point you can cover and refrigerate for 24 hours. Then preheat oven to 350 and proceed with the recipe.

Brush with milk and sprinkle with reserved buttered potato topping mixture.

Bake at 350° for 35 minutes or until golden brown. Cut into wedges to serve.

Yield: 10 servings.