Preheat the oven to 350°F (175°C) and line a muffin tin with cupcake liners.

In a mixing bowl, cream together the softened butter and granulated sugar until light and fluffy.

Add the eggs one at a time, mixing well after each addition.

Stir in the buttermilk, lemon juice, and lemon zest until combined.

In another bowl, whisk together the flour, baking powder, baking soda, and salt.

Gradually add the dry ingredients to the wet ingredients, mixing until just combined.

Fill the cupcake liners about 2/3 full with the batter.

Bake for 15-18 minutes or until a toothpick inserted into the center comes out clean.

Allow the cupcakes to cool completely on a wire rack.

In a mixing bowl, beat the softened butter until creamy.

Gradually add the powdered sugar, mixing well until smooth.

In a small saucepan, heat the blueberries over medium heat until they break down and release their juices.

Strain the blueberries to remove the skins and add the juice to the buttercream.

Add the heavy cream and vanilla extract, mixing until well combined and fluffy.

Once the cupcakes are completely cool, frost them generously with the blueberry buttercream.

Decorate with fresh blueberries if desired.