Preheat oven to 325°F. Spray a 10-inch bundt pan with non-stick spray.
In the bowl of a stand mixer fitted with the paddle attachment, cream butter until smooth (about 3 minutes). Gradually add the sugar and mix until light and fluffy.
Add the eggs, one at a time, mixing well after each addition.
Slowly add the cake flour. Mix until combined.
Remove the bowl from the stand mixer and pour in the buttermilk. Mix by hand until just incorporated. Use a spatula to scrape down the sides of the bowl to incorporate all ingredients.
Stir in the lemon extract and lemon zest. Gently fold in blueberries.
Pour the batter into the prepared bundt pan. Bake for 85-90 minutes, or until a toothpick inserted into the center of the cake comes out with a few crumbs, but no wet batter. The crust will be a dark golden brown around the edges and lighter in the center. Allow cake to cool to room temperature.
In a small bowl, combine confectioners' sugar and lemon juice. Mix until smooth. Pour over the cooled cake.
