In a medium bowl, add all the glaze ingredients. Mix to form a thick glaze, since different brands of blueberries will absorb liquid differently, feel free to add more heavy cream or confectioner's sugar to get the consistency you want. It should be thick enough to stick to the back of a spoon an slowly drizzle off the spoon. Dip each doughnut, while warm into the glaze, making sure to coat both sides. Place on a wired rack with a parchment paper underneath to catch the extra glaze.
Add vegetable oil to an 8-quart stock pot is an large dutch oven. While making the dough slowly start to heat the over medium heat; you want it to reach somewhere between 365°F and 375°F before you begin to cook.
In medium bowl, add the dry ingredients and set aside (flour, ground freeze dried-blueberries, baking soda, baking powder and salt.
In a separate large bowl, beat the eggs, buttermilk, and sugar and until combined, mixture should be light in color an slightly thickened. Fold in the melted butter. Add in the reserved dry ingredients and fold to form a thick but soft dough. It will be slightly sticky. Flour a work surface, and your hands, and turn the dough out onto the surface. Knead the dough four or five times to make it cohesive and incorporate the blueberries into all parts of the dough. Then, with a well-floured rolling pin, roll the dough out until it's about 1/2-inch thick.
With a circular cookie cutter (I used a 3.5 inch cutter) dipped in flour (you will want to re-dip it in flour each time you cut), cut out doughnuts. Save the "holes" for munchkins! I don't recommend re-rolling the dough.
When the oil is 365°F to 375°F, use. a slotted spoon to lower one doughnuts into it. I recommend starting with one to gage your cook time before moving into batches of 3 or 4 doughnuts at a time. The doughnuts may initially sink to the bottom of the pot, but they will quickly rise up again. Fry the doughnuts until lightly golden brown, about a minute. one each side. Then flip them and cook for a final 30 seconds.
Remove the cooked doughnuts from the oil and place on a paper towel lined plate to catch the excess oil. Dip in glaze immediately .
Store cooled doughnuts, well wrapped, at room temperature for up. to 3 days.