Fascinating Maeve, I love food history. So evocative. Have another lovely book here at home which details the vast array of recipes belonging to the Jewish diaspora and how they morphed and changed according to what was available in different continents.

An Australian "Irish Soda Bread" shows a very similar enrichment of of the original plain Irish variety to the US version. This one has melted butter, sugar and egg in, making it a kind of rich sweet tea bread:

Australian 'Irish soda bread'