Preheat oven to 375°F. Line a 12-count cupcake tin with cupcake liners.
In a medium mixing bowl, whisk together the flour, baking powder, and salt. Set aside.
In a separate large mixing bowl, add the butter and sugar. Using a hand mixer, beat on medium-high speed until light and fluffy, about 2 minutes.
Add in the eggs one at a time, beating each egg until fully incorporated after each addition. Add vanilla and lemon zest. Beat until combined.
Alternating between the flour mixture, milk, and lemon juice, add each to the butter mixture, beginning and ending with the flour mixture. Beat until just combined, making sure not to overmix.
Fill the prepared cupcake liners about ¾ full. Bake about 12-15 minutes, or until a toothpick inserted in the center comes out mostly clean. Let the cupcakes cool in the pans for about 10 minutes before removing them to finish cooling on a rack.
While the cupcakes are cooling, prepare the buttercream.