Preheat oven to 350 degrees F.
Line a muffin tin with cupcake liners and set aside.
Mix the unsalted butter and sugar until creamy. Add the eggs, sour cream, and buttermilk and mix until well incorporated.
Add the all-purpose flour, salt, baking soda, and salt. Mix until well combined but do not over mix.
Fold in the fresh blueberries. Fill each cupcake liner about 3/4's of the way full.
Bake the cupcakes for 17 minutes or until fully cooked through.
Let the cupcakes cool completely before frosting. To make the frosting, mix the unsalted butter and cream cheese for 2-3 minutes. Add the vanilla extract and powdered sugar. Mix for 3-4 minutes or until fluffy.