Center a rack in the oven to 350°F. Prepare two cupcake tins by using liners or spray with non-stick cooking spray.
Whisk together the flour, baking powder and salt in a medium bowl.
Whisk together the milk, lemon juice and egg whites in a separate bowl.

Put the sugar and lemon zest in a mixer or another large bowl and thoroughly mash it up with a whisk until the sugar is moist and fragrant. Use the same whisk from steps 2 and 3. No need to dirty more stuff. Add the butter and, working with the paddle attachment, or with a hand mixer, beat at medium speed for a full 3 minutes, until the butter and sugar are very light. It will clump up at first, but will soften and gain volume the more you beat it.

Add in the extracts and one third of the flour mixture and beat on medium speed just until combined. Beat in half of the wet mixture, then another third of the dry, the rest of the wet, and finally the remaining dry ingredients until incorporated. I like to stop the machine for each addition and stir the mixture in by hand for a few seconds first to avoid wearing half of it when I turn the machine back on.

Finally, give the batter a 30 second beating to ensure that there are no lumps left and scoop/pipe the batter into the cupcake tins, filling each well 2/3 full.
Bake for about 18 minutes, or until a toothpick inserted into the cupcakes comes out clean. Cool on wire rack.

Using a mixer, blend the butter and cream cheese together until light and fluffy.
Gradually add in the confectioners' sugar until fully incorporated.
Mix in vanilla, lemon juice and any food coloring, if using, and beat until smooth.
Taste the frosting and add more confectioners' sugar if you like your frosting thicker or sweeter.
Spread or pipe onto cooled cupcakes, and enjoy!

if you are in a humid country like mine, it is better to put your mixing bowls and whisk in the fridge to cool, so that your frosting will not melt.

but if you use the right butter you won't have any problem. never use margarine in your frosting because it will not whip up.