Combine 1 cup flour, sugar, undissolved yeast, and salt in a large mixer bowl. Heat milk and 2 tablespoons butter until very warm (120o to 130oF). Add to flour mixture with egg. Beat 2 minutes at medium speed of electric mixer, scraping bowl occasionally. Stir in enough remaining flour to make a soft dough. Knead on lightly floured surface until smooth and elastic, about 6 to 8 minutes. Cover; let rest 10 minutes. Roughly chop 2 of the candy bars. Set aside. Roll or pat dough to 12 x 6-inch rectangle (about 1/2-inch thick); spread with 3 tablespoons softened butter. Sprinkle with graham cracker crumbs and the chopped candy bars, gently pressing into the dough. With sharp knife, cut dough lengthwise in half. Stack both halves; cut crosswise into 6 pieces. Arrange stacks, standing up with longer cut sides on bottom of greased 9 x 5-inch loaf pan. (This will be messy and some of the graham cracker crumbs and chocolate may fall off. Sprinkle any stray crumbs and chocolate over top of loaf.) Cover; let rise in warm, draft-free place 30 to 35 minutes, until loaf has risen just to the edge of the pan. (It should not double). Bake in a preheated 350°Foven for 30 minutes. If loaf is getting too brown, cover with a piece of foil. Carefully sprinkle loaf with marshmallows and bake an additional 3 to 5 minutes until marshmallows are lightly browned. Remove from oven. Cool in pan 10 minutes. Carefully remove from pan and place loaf on a wire rack. Melt remaining candy bar and drizzle over loaf. Serve immediately.