Shortbread is a type of biscuit or cookie.
It is traditionally made from one part white sugar, two parts butter, and three parts flour (by weight).
The use of plain white (wheat) flour is common today, and other ingredients like ground rice or cornflour are sometimes added to alter the texture.
Also, modern recipes often deviate from the pure three ingredients.
This is done by splitting the sugar portion into equal parts granulated sugar and icing sugar (powdered sugar in American English) and many further add a portion of salt. (source)
So can hamsters eat shortbread?
It is not the best for hamsters to eat as it contains too much sugar for them.
The best biscuits for them to nibble on are those that are low in sugar.