Preheat oven to 350*F. Prepare a cupcake with paper liners. Set aside.
In a medium bowl, add cake flour, baking powder, baking soda and salt. Stir together with whisk, and set aside.
In the bowl of an electric mixer, add eggs and beat 10-20 seconds. Add sugar and continue to beat on medium speed about 30 seconds. Add vanilla extract (and lemon extract if using) and oil, beat until smooth and combined.
Reduce mixer speed to low and slowly add about half of the flour mixture. Add the milk, then the rest of the flour and the sour cream (and lemon zest if using). Beat until just combined. Scrape down the side of the bowl.
The batter will be thin. Pour batter into prepared pan with liners. Fill liners about 2/3 full.
Bake cupcakes for 12 to 14 minutes.
Cool in pan 1-2 minutes, then remove cupcakes from pan (carefully) and finish cooling on a wire rack.
Frost as desired when fully cool.