Butter and margarine are two completely different ingredients that are not interchangeable. One does not substitute for the other.
Scotch shortbread illustrates this perfectly. There are three ingredients: Butter, flour and sugar. Shortbread depends on butter, its raison d’etre, reason for being. Originally, shortbread was the result of the Scotch farmer’s wife enjoying her butter churned from the milk of her cows who ate the succulent grasses of the countryside.
There’s no vanilla nor lemon juice, its not necessary. The richer (higher butterfat) and sweeter the butter, the more delicious is the cookie.
Following is an example:
* 2 cups sifted self-rising flour
* 1 cup unsalted butter (try a premium brand)
* 3/4 cup sugar
Use a pastry blender, or your fingers, to blend butter into flour. It should be nicely combined into small particles when sugar is stirred in with a wooden spoon.
Knead on a floured surface; it will be very soft. Divide in half and press into two 9 x 5″ pans that have been lined with parchment paper. Bake at 350-degrees for about 20 minutes, until set but not browned.
Allow to cool slightly, not completely, and cut into small squares. When thoroughly cooled, dust with powdered sugar. This makes about 15 squares, but the recipe will double.
OTHER NICE COOKIES
There are many recipes for nice cookies made with margarine, flour, sugar, sometimes eggs, and flavorings. They are not shortbread, and should be enjoyed for what they are: Nice cookies, but not shortbread.