Preheat oven to 350°F. Line a cupcake pan with paper liners.
In a medium bowl, add 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. The mixture should be thick and fluffy. Add vanilla and oil, beat.
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. Beat until just combined. Scrap down the side of the bowl.
The batter will be thin. Pour (or scoop) batter into a cupcake pan prepared with paper liners. Fill liners about 2/3 full.
Bake cupcakes in pre-heated oven for 12-14 minutes. Watch cupcakes carefully. The cupcakes are baked when the tops have a slight dome and the tops no longer appears moist in the center. The edges should be golden brown.
Prepare frosting
In the bowl of an electric mixer, beat butter (while still cool) until smooth.
Add (cold) cream cheese and continue to beat until fully incorporated and smooth.
Add powder sugar, one cup at a time, while the mixer is running.
Continue mixing and add lemon zest, vanilla and lemon juice (and food coloring if using). Mix an additional 30 seconds, until smooth, light and fluffy.
Flour - Be sure to measure the flour properly. Flour should never be packed into the measuring cup. I would suggest using a whisk to fluff up the flour in the bag or canister (whichever container you use to store your flour), then scoop the measuring cup into the flour. Fill to overflowing (without compacting), then level off the measuring cup with the back of a butter knife.As an alternative, and for an extra tender and fluffy texture, use Cake Flour in place of the All Purpose Flour. For this recipe use 1 1/2 cups sifted cake flour in place of the 1 1/4 cups all purpose flour.Use at once or keep refrigerated. (This frosting will keep well in the refrigerator for several days, but you may need to re-beat it for the best texture). Top frosted cupcakes with pretty Easter candies if desired.