½ cup unsalted butter, cubed and at room temperature
4 cups confectioner's sugar, divided
2 tablespoons whole milk, or more as needed
Instructions
Assemble buttercream following the steps as outlined here, subbing blackberries for the black raspberries (but of course use black raspberries, if you have them!) and erring on the side of more lemon zest, when in doubt.
Recipe by the pig & quill at https://thepigandquill.com/vanilla-cream-cheese-cupcakes-with-blackberry-lemon-buttercream/