Preheat your oven to 350 degrees F (175 degrees C). Spray a bundt pan well with non-stick cooking spray, dust with flour, and shake out the excess.
In a mixing bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt for about 20 seconds.
In the bowl of an electric stand mixer, mix together granulated sugar and lemon zest until pale yellow and fragrant, about 1 minute.
Add softened butter and whip until pale and fluffy, about 3 to 4 minutes.
Blend in eggs, one at a time, mixing well after each addition. Mix in lemon extract.
In a separate measuring cup, stir together buttermilk and lemon juice. Toss blueberries with 1 tablespoon of flour mixture and set aside.
Add 1/3 of the flour mixture to the butter mixture, mixing just until combined. Then add half of the buttermilk mixture, mixing just until combined. Repeat this process.
Gently fold in blueberries with a spatula, being careful not to crush them.
Pour batter into prepared bundt pan and bake for 50 to 60 minutes, or until a skewer comes out clean.
Cool in the pan for 20 minutes, then run a sharp knife around the edges before inverting onto a wire rack.
To make the icing, mix cream cheese and butter until smooth. Gradually add powdered sugar and lemon juice until fluffy.
Once the cake is cool, spread the icing over the top and decorate with extra blueberries, lemon slices, and mint leaves.