Among other things that separate cranberries and blueberries (like color and tartness), a fresh cranberry floats because it has air in it, and a fresh blueberry sinks. Which is probably fine, if you’re trying to wash it, but when mixed into, say, a cake batter, it means your blueberries end up arranged all along the bottom of the cake.
That’s why nearly every blueberry cake recipe includes the same step: toss the blueberries in flour to make it easier for the batter to hold on to them.
Here’s a version from the August 10, 1888 edition of the Fitchburg (Massachusetts) Sentinel:
Blueberry Cake — Cream a cup of butter and two cups of sugar, and add the yolks of five eggs thoroughly beaten, a cup of milk, a teaspoonful of cinnamon, half a nutmeg grated, three cups of flour containing two teaspoonfuls of baking-powder, the whites of the eggs beaten stiff and a scant quart of blueberries dredged thickly with flour. Bake in shallow tins.
Now, something blueberries do have in common with cranberries is that they travel by different names. Cranberries are also known as bearberries, and blueberries have names like bilberries, hurtleberries, and whortleberries.
Here’s whortleberry cake from the July 19, 1883 edition of The Bucks County Gazette of Bristol, Pennsylvania:
Whortleberry cake without eggs is economical as well as very nice. To one quart of flour allow one cup of sugar, one pint of berries, a little salt and three teaspoonfuls of baking powder; use sweet milk to wet them up with. The berries should be washed and drained in a colander before putting them in the dough. Roll out and bake as you do biscuit; or you may bake in a narrow but deep tin, and serve in slices. This is relished when warm or cold.
From a box sold in Winsted, Connecticut.
Aunt Elija’s Blueberry Cake
2/3 pint milk
1 tsp. cream of tartar
1/2 tsp. baking soda
4 Tablespoons melted lard or shortening
1 cup brown sugar and flour to stiffen
Put berries in milk and shortening. Have 1 cup flour and rest of dries mixed. Add milk and berries. More flour if necessary.