In a large mixing bowl, whisk together 2 cups of all-purpose flour, 1 cup of granulated sugar, 2 teaspoons of baking powder, 1/2 teaspoon of baking soda, and 1/2 teaspoon of salt until well blended.

In a separate bowl, cream together 1/4 cup of softened butter and the remaining sugar until fluffy, about 3 minutes. Add in 1 large egg and 2 teaspoons of vanilla extract, mixing until combined. Slowly pour in 1 cup of whole milk while continuing to mix until the batter is smooth and airy.

Gently fold the wet mixture into the dry ingredients using a spatula until just combined. Be careful not to overmix. Once incorporated, delicately fold in 1 cup of fresh blueberries.

Preheat your oven to 350°F (175°C) and grease a donut pan. Carefully spoon the batter into the donut pan, filling each cavity about three-quarters full.

Place the filled donut pan in the preheated oven and bake for about 25 minutes, or until edges are golden brown and a toothpick inserted in the center comes out clean.

Once baked, remove the pan from the oven and let it cool for about 5 minutes before gently transferring the donuts to a wire rack to cool completely before glazing.