This is from a time when ingredients were not so plentiful. My great grandmother was born in 1848 so it has been around a long time. My mother used to make it as well as her mother. My family has enjoyed it for years and I hope you will enjoy it too.
Cream butter until light, then add sugar and continue beating until fluffy then add the egg. Mix baking soda with the flour and add alternately with the milk. The batter will be very stiff but it needs to be to support the load of blueberries. Stir in the blueberries then spread into a sprayed 9x9 and bake at 325 for 45 to 50 minutes or until browned and pulled away from the sides of the pan. Cool completely before cutting. (If using frozen blueberries you will need to add 10 to 15 minutes more time.)