Originally Posted by jennyema
If this is so, shouldn't you use 20% less butter?
No, Jennyema - the amount of fat is the same in the two on a volume to volume substitution .... but Shirley and Alton would both make me sit in the corner for not remembring this until your question:
You have to adjust the liquid content to compensate for the differences between the two - shortening is fat and air, butter is fat and water. Using US measurements (1 cup = 16 Tablespoons, 1 Tablespoon = 3 teaspoons) ... the factor is 1.5 teaspoons liquid per 1/4 cup. If you are substituting butter for shortning you subtract that amount of liquid from the recipe, if your substituting shortning for butter you add that much water.
So, in this case of swapping 3/4 cup butter for 3/4 cup shortning - Ally should reduce the liquid in the recipe by 4.5 teaspoons (or 1 Tablespoon plus 1.5 teaspoons).