Preheat your oven to 350°F (175°C). Line a 12-cup muffin tin with paper liners and set aside.
In a medium bowl, whisk together the flour, baking powder, baking soda, and salt until evenly combined. Set this dry mixture aside.
In a large mixing bowl, beat the softened butter and sugar together with an electric mixer on medium speed for 2-3 minutes until light and fluffy.
Add the eggs one at a time, beating well after each addition. Mix in the lemon zest, lemon juice, and vanilla extract until fully incorporated.
With the mixer on low speed, alternate adding the dry ingredients and buttermilk to the butter mixture, beginning and ending with the dry ingredients. Mix just until no flour streaks remain—do not overmix.
Divide the batter evenly among the prepared cupcake liners, filling each about two-thirds full. Bake for 18-20 minutes, until a toothpick inserted in the center comes out clean and the tops spring back when lightly pressed.
Remove cupcakes from the pan and let them cool completely on a wire rack, about 45 minutes, before frosting.
For the frosting, beat the softened cream cheese and butter together on medium speed until smooth and creamy, about 2 minutes.
Gradually add the powdered sugar one cup at a time, beating on low speed until incorporated, then increase to medium-high and beat until fluffy. Mix in the lemon juice and zest until smooth.
Frost the cooled cupcakes using a piping bag fitted with a large star tip, or spread the frosting on with an offset spatula. Garnish with additional lemon zest if desired.
