In stand mixer bowl, combine 2 1/2 cups flour, yeast, sugar and salt; mix well. Add warm water, shortening and egg to flour mixture. Using a paddle attachment, blend at low speed until moistened; beat 2 minutes at medium speed. Gradually stir in remaining flour to make a stiff batter. (NOTE: For hand mixing: following above steps, mix ingredients in large mixing bowl using a wooden spoon or dough whisk.)
Cover; let rise in warm place until almost doubled, about 30 minutes.
Prepare pan: Grease a 13x9-inch cake pan; set aside.
Stir down batter. Spread evenly in prepared pan. Cut wieners in half, lengthwise; press down into batter. Cover; let rise in warm place until double, about 25 minutes.
Preheat oven to 375°F.
Bake for 25 to 30 minutes until golden brown. Brush with butter. Serve warm with mustard.