Combine yeast, sugar, salt, and 2 cups flour in large mixing bowl.
Stir together shortening, butter, and 1 cup boiling water until melted. Cool to 120°-130°.
Add butter mixture and lightly beaten egg to flour mixture, and beat at medium speed with a heavy duty mixer 1 minute. Remove beater, and replace with dough hook attachment. Add remaining 1 1/2 cups flour, beating 3 to 5 minutes. Cover and let rise in a warm place (85°), free from drafts, 1 hour or until dough is doubled in bulk.