Briefly on the history of the shortbread recipe
British sugar import started ca. 1650. First published recipe for "short bread", based on web archives, is from the book Cookery and Pastry By Susanna MacIver, Edinburgh 1773:
To make Short-Bread.
Take a peck (=9.1 litres) of flour, and four pounds of butter English, or three pounds Scots, weight; put the butter on to come a-boil; make a hole in the flour, and pour the boiling butter in it; work the flour and butter a little while together; pour in a mutchkin of good yest amongst the paste; work it together, but not too much; divide the paste and roll it out oval; then cut it through the middle, and plait it at the ends; keep out a little of the flour to work out the bread; flour gray paper, and fire the bread on it: if you make it sweet, allow a pound (Scots or English?) of sugar to the peck of flour at least; if you want it very rich, put in citron, orange-peel, and almonds, and strew white carvy on the top; be sure to mix the sugar and fruit with the flour before you wet it; remember to prick it well on the top.
The recipes we see today tend to follow a sugar-butter-flour weight ratio of 1:2:4. It seems that this was established around 1850. Here from the book Cookery and domestic economy By Mrs. Mary Somerville, 1862 Glasgow:
Plain Shortbread (referred to as 'Scottish' in other books)
4oz castor sugar
8oz butter
16oz flour
Rice Shortbread
4oz castor sugar
8oz butter
8oz flour
8oz rice flour
Almond Shortbread
4oz castor sugar
8oz butter
12oz flour
1oz almonds (ground+flour)
I tried to find an early recipe that uses less flour. Here is the only one I was able to find, using a 2:3:4 weight ratio, from the magazine The Girl's Own Paper, Vol. XX, No. 995, January 21, 1899:
Shortbread.
Ingredients.—One pound of flour, three-quarters of a pound of butter, half a pound of castor sugar.
Method.—Rub six ounces of the butter into the flour and sugar, melt the rest and mix it in; work a little with the hands to form a dough; roll into two thick rounds and pinch them round the edge with the fingers to ornament them. Prick over the top with a fork or a biscuit pricker; put two or three large pieces of candied peel on each and bake about half an hour in a moderate oven.
(Interestingly, this method seems copied from Mrs. Somerville's 1862 Almond Shortbread recipe.)