ound, my Mom always makes them for Christmas. 
I did a little research on the history of shortbread, and found they go all the way back to 12th century Great Britain - originating as a "biscuit bread" made from left-over bread dough. Eventually butter was used as the shortening which made them quite a luxury item since butter was expensive. It is the large amount of butter that makes them crumbly like a shortcrust pastry (and divine tasting!) The other core ingredients are flour and sugar, although flavorings such as caraway, lemon and almond extract have also been added - which makes me think - rosewater would give them a delicate, aromatic quality - will give this a try this next time!
This recipe also includes cornstarch (called corn flour in the UK) - ironically a New World ingredient, but it gives the shortbread a more tender texture, as does the confectioners sugar. Shortbread typically comes in three different shapes:  small round biscuits, fingers (the method we use) or large rounds.  Fork tines are always used to create a lattice pattern on the top too. 
Regular granulated sugar is supposed to be sprinkled over the shortbread, but when I made it last week I jazzed it up for spring with some pink and yellow dusting sugar. No matter how this recipe is served up, it is always a winner! 

Shortbread

2 sticks butter (has to be real butter - do NOT use margarine!)
2 cups plain flour
1 cup cornstarch
1 cup confectioners sugar

Melt butter in saucepan over low heat. Remove from heat and add flour, sugar and cornstarch. Mix well (may need to use hands to mix). Put in a 8 x 11 pan and prick all over with a table fork. Bake in a 275-300 oven for 45-55 minutes (edges can brown so check after 45 min). Sprinkle with sugar and cut into finger shapes immediately (if you wait to cut them they will crumble). Cool then store in an airtight container.