Pre-heat oven to 350F. Place 15 cupcake cups (see note) on a baking pan, evenly spaced about 1-2 inches apart. No need to grease the cups or the pan. Set aside.
Using a stand mixer fitted with the whisk attachment or a handheld electric mixer, whisk the 10 egg whites on medium speed until foamy.
Add 1/2 teaspoon cream of tartar and continue whisking until soft peaks form.
Gradually (slowly and in small quantities at a time - do not dump all the sugar in) add the 3/4 cup sugar and whisk until you reach stiff peaks.
Once the meringue is ready, transfer it to a piping bag fitted with a large star tip (you can also use a large Ziploc bag with one of the corners cut off). Using a circular, upward motion (see video), pipe the meringue into the cups (overflowing by about an inch on top). Remember to leave a slight gap in the middle where you can fill the custard later.
Place the cookie sheet with your cupcakes into your pre-heated oven and bake for about 20-25 minutes or until the tops turn light brown (see note).
Take out of the oven and allow to cool slightly before piping the custard filling (instructions below).
Finish by sprinkling with confectioner's sugar.
For the Custard:
In a medium heavy-bottom saucepan (don’t turn on the stove yet), beat the 10 egg yolks before adding all the condensed milk.
Mix them thoroughly then start cooking over low heat. Stir often so you don't end up with scrambled eggs.
When you see that your mixture is starting to take shape and form into clumps, add the 1 teaspoon of vanilla and the 1 teaspoon of lime juice.
When you’ve reached custard consistency (thick but still spreadable), turn off the stove, remove pan from heat and set aside until you're ready to pipe the custard into your cupcakes.
Depending on how much meringue you put into your cups, you may need more (or less) than 15 standard size cupcake cups.Every oven is different so I'd suggest you check at the 20-minute mark (not earlier, you don't want to mess with your oven's temperature too much too soon). Take a cupcake and check if the insides are cooked. If it still appears soupy, adjust the time accordingly. My cupcakes are cooked right at 22 minutes.