Line a baking sheet with parchment paper. Set aside.
In a large bowl, combine the flour, sugar, baking powder, baking soda, salt, cinnamon, and nutmeg together. Set aside.
3½ cups all-purpose flour, ¾ cup granulated sugar, ½ teaspoon baking powder, ½ teaspoon baking soda, ½ teaspoon kosher salt, 1 teaspoon ground cinnamon, ¼ teaspoon ground nutmeg
In a medium bowl, whisk the eggs, milk, sour cream, and vanilla together. Add the melted butter and whisk to combine.
2 large eggs, ¾ cup milk, ¼ cup sour cream, 1 teaspoon pure vanilla extract, ¼ cup unsalted butter
Add the wet ingredients to the dry ingredients. Stir until smooth.
Gently fold in the blueberries.
1⅓ cups fresh blueberries
Roll out the dough on a well-floured surface to about ½-inch thickness.
Using a donut cutter (or 2 round cookie cutters), cut out the donuts. For clean cuts, dip the cutter into flour before pressing into the dough. Save the centers for donut holes. Roll the dough scraps together and repeat until the dough is used up. Arrange the donuts and donut holes on the prepared baking sheet.
Heat 2 inches of oil in a Dutch oven to 350-360°F. While the oil heats, line a baking sheet or wire rack with paper towels.
Vegetable oil
Once the oil is hot, fry the donuts. Working 2-3 donuts at a time, drop the donuts into the oil and cook for 2 minutes on each side, until golden. (Watch the donut holes closely as they will take less time to cook.) Remove the donuts from the oil and place on the paper towel-lined tray. Repeat until all donuts are fried.
Let the donuts cool slightly.
Make the glaze. In a medium bowl, whisk the powdered sugar, milk, and vanilla together.
2 cups powdered sugar, ¼ cup milk, ½ teaspoon pure vanilla extract
Dip each donut into the glaze. Place glazed donuts on a cooling rack and let the glaze set for about 10 minutes before serving. Serve and enjoy!