Preheat the oven to 350 degrees. Butter and flour a 9- inch x 13- inch pan.
In the bowl of your mixer, cream together molasses and butter.
Beat in the egg.
Whisk together the dry ingredients, add to creamed mixture, beating to combine.
Stir in 1 cup of boiling water. Scrape sides and mix well.
Fold in the frozen wild Maine blueberries.
Spoon into prepared pan, smoothing the top. Bake until a toothpick comes out clean, about 30 minutes.
Let cool on a rack.
Cut into squares and serve with whipped cream.