Preheat the oven to 350°F. Line a cupcake pan with cupcake liners.
In a large bowl, whisk together the flour, baking powder, and salt.
In a large mixing bowl, cream together the butter and sugar with an electric mixer for 3 minutes, or until fluffy. Add the eggs 1 at a time and mix just until combined. Once mixed, add lemon zest, 3 Tablespoons lemon juice, and vanilla. Mix until incorporated. Use a rubber spatula to scrape sides of the bowl until batter is well combined.
Slowly add the flour mixture, alternating with the buttermilk. Mix just until combined. With a rubber spatula, gently fold in blueberries.
Using a large cookie scoop, add batter to the cupcake pan until the tins are about 3/4 full. Bake 18-22 minutes, or until a toothpick inserted in the center comes clean. Let cool completely.
Lemon Frosting
In a stand mixer fitted with the paddle attachment, cream together the butter and cream cheese. Beat until fluffy.
Add the powdered sugar, 2 tablespoons lemon juice, zest, vanilla, and salt. Mix until creamy. If you need to thin the frosting, add a dash of milk. If you want to thicken it, add a couple Tablespoons powdered sugar.
Once cupcakes are cooled, pipe or spread the frosting on top of each cupcake.
Top frosted cupcakes with blueberries and lemon zest, if desired.
Notes
Blueberries: If using frozen, do not thaw first. You can also mix the blueberries with a teaspoon of flour to prevent them from sinking. Butter and cream cheese: Make sure to leave both of these out an hour before making or follow these tips on how to soften butter and how to soften cream cheese. Learn how to frost the perfect cupcakes.