Preheat oven to 350°F. Line a baking sheet with parchment paper, set aside. Spray a doughnut pan with non-stick cooking spray, set aside.

Make the crumb topping. In a large bowl combine the flour, brown sugar, granulated sugar, salt, cinnamon and nutmeg. Add the butter and cut in with a pastry blender, fork, two knives, potato masher or your hands, until the mixture is crumbly and coarse crumbs form, about the size of peas. Spread the crumb topping onto the prepared baking sheet and give it a good shake to spread it out evenly. Bake for about 20 minutes, tossing halfway through baking, or until it begins to brown. Remove from oven and allow to cool down completely. Run your fingers through the topping to break up any large clumps. Set aside.

Make the doughnuts. In a medium bowl, whisk or sift together the flour, baking powder, baking soda, and salt. Set aside. In a large bowl, cream together the butter and sugar for about 5 minutes, or until light and fluffy. Add the eggs, one at a time, mixing well after each addition. Stir in the vanilla extract. Add the dry ingredients, alternately with the buttermilk, making sure to start and end with the dry ingredients. Mix until just combined. Fold in the blueberries. Spoon the batter into the prepared doughnut pan and bake for about 10 to 12 minutes or until the doughnuts are golden brown on the edges and a toothpick, inserted in the middle, comes out clean. Remove from oven and allow to cool in pan for about 10 minutes. Remove the doughnuts, place on a wire rack and allow to cool completely. Repeat with the remaining batter until all the doughnuts are baked.

Make the glaze by mixing together the powdered sugar and enough milk to make it a smooth spreading consistency. Once all the doughnuts are fully cooled, you can dip them into the glaze and then into the crumb topping from earlier. Place back on the wire rack and allow the glaze to set before eating. Store any leftovers in an airtight container. Will keep for up to 4 days. Enjoy!