Preheat your oven to 350°F (175°C) and grease a 9x13-inch baking dish.
In a large bowl, whisk together the flour, granulated sugar, baking powder, and salt.
In another bowl, cream the softened butter until smooth.
Add the egg, milk, and vanilla extract, mixing until well combined.
Gradually add the dry ingredients to the wet mixture, stirring until just combined.
Gently fold in the wild blueberries.
In a small bowl, mix the cinnamon and brown sugar together.
Spread half of the batter into the prepared baking dish.
Sprinkle half of the cinnamon-sugar mixture over the batter.
Pour the remaining batter on top and sprinkle with the rest of the cinnamon-sugar mixture.
Bake for 30-35 minutes or until a toothpick inserted in the center comes out clean.
Allow the coffee cake to cool for about 10 minutes.
In a small bowl, whisk together the powdered sugar and lemon juice to create a glaze.
Drizzle the glaze over the warm coffee cake before serving.