To make your Lemon Cupcakes, preheat oven to 375 degrees F and line 24 cupcake pan cups with paper liners.
Sift the flour, baking powder and salt together in a bowl. In another bowl, beat the softened butter and sugar with an electric mixer until light and fluffy. Beat in the eggs one at a time, beating each egg until incorporated before adding the next. Mix in the vanilla extract, lemon juice and lemon zest.
Gently mix the flour mixture into the butter mixture, one third at a time, alternating and add the milk. Beat until just combined; do not over mix.
Fill the prepared cupcake liners with batter 3/4 full, and bake in the preheated oven until a toothpick inserted in the center comes out clean, about 17 minutes. Let the cupcakes cool in the pans for about 10 minutes before removing them to finish cooling on a rack.
To make your Lemon Buttercream Frosting, in a medium sized mixing bowl, sift the powdered sugar. Add the softened butter and cream together on low speed until the powdered sugar and butter are completely combined. Add in a pinch of salt and then the lemon juice and zest.
Continue to beat on medium speed until the frosting is light and creamy. If frosting is too thin, add a bit more powdered sugar. If it is too thick, add a tablespoon of water or milk to thin it out.