In covered small saucepan, cook squash in a small amount boiling water about 20 minutes or until very tender. Drain and cool.
Grease twelve 2-1/2-inch muffin cups; set aside.
Meanwhile, in medium bowl, combine flour, sugar, baking powder, and salt. Make a well in the center of the flour mixture; set aside.
In small bowl, combine egg, milk, shortening, and cooked squash. (Shortening and squash will break up when stirred into flour mixture). Add squash mixture all at once to the flour mixture. Stir just until moistened (batter should be lumpy). Spoon batter into prepared cups, filling each 2/3 full. Bake in a 400 degree F oven about 18 minutes or until golden. Cool in pan on a wire rack for 5 minutes. Remove from muffin cups; serve warm. Makes 12 muffins.