Preheat the oven to 325F (170C) degrees and line a muffin pan with muffin papers. You will end up with 12-14 cupcakes for this recipe.
In a medium bowl whisk together the flour, baking powder and salt.
In a large bowl using an electric mixer, beat the butter, sugar and lemon zest until fluffy (about 2-3 minutes).
Add in the vanilla extract and beat in the eggs 1 at a time.
Beat about 1/3 of the flour mixture into the butter mixture, followed by the sour cream. Turn off the mixer and scrape down the sides of the bowl as necessary.
Beat in another 1/3 of the flour mixture, followed by the milk. Scrape down the sides and bottom of the bowl, along with the beaters.
Beat in the rest of the flour mixture stopping as soon as it's incorporated, or whisk in using a wire whisk.
Whisk in the lemon juice.
Spoon the batter into the prepared muffin pan, filling each liner about 3/4 full. You should end up with about 12-14 cupcakes total. Do not fill the liners to the top or the cupcakes will overflow.
Bake one tray at a time on the middle rack of your oven for 18-20 minutes, or until an inserted toothpick comes out clean.