Step 1

Line three muffin tins with paper cupcake liners, and preheat the oven to 350°F.

Step 2

Place the graham crackers into a ziplock bag, and use a rolling pin to crush them into fine pieces. There shouldn't be any large chunks remaining.

Step 3

In a mixing bowl, combine the graham cracker crumbs, melted butter, sugar, and salt. At first, the butter may stick to the crumbs in clumps, but keep stirring until the mixture is fully amalgamated. After a bit of mixing, it will resemble wet sand.

Step 4

Using your handy bar muddler, press a large spoonful of crumbs into each lined well of the muffin tin. Tamp down well, creating a nice, solid graham cracker crust.

Step 5

Bake the crusts for 7-8 minutes. They will be slightly golden brown when finished. Set aside and let cool while you prepare the cupcake batter.

Step 6

Into a medium-sized bowl, sift the flour, baking powder, and baking soda. Set aside.

Step 7

Beat the softened butter and sugar together on high for a few minutes, until the mixture is fluffy and light.

Step 8

Into the bowl of your mixer, add the room temperature eggs and vanilla. Beat again until everything is combined.

Step 9

Dump about a third of the flour mixture into the wet ingredients, and then pour in a third of the milk. Use a spatula to stir the batter until it just begins to come together. Repeat the process twice more, alternating between flour and milk. Stir carefully, distributing all the ingredients well, but taking care not to overmix the batter.

Step 10

Using a quarter-cup sized measure, portion the batter evenly among the lined muffin tins. Remember, the graham cracker crust should be baked before adding the cupcake batter.

Step 11

Place your cupcakes in the preheated oven (350°F) and bake for 28 minutes. Refrain from opening the oven prematurely, as letting the heat out can cause the cupcakes to deflate before forming enough structure to form a pretty domed top. When the timer is finished, use a toothpick to check for doneness. Moist crumbs are okay, but no wet batter should remain. If the cupcakes aren't fully cooked, let them bake for a few more minutes, testing again, before removing from the oven.

Step 12

Let the cupcakes cool in their tins for about ten minutes, then gently release to a cooling rack. Let them fully cool before moving on to the next steps. If you need to store the cupcakes overnight, do so in a covered container at room temperature.

Step 13

Bring some water in a small pan to a simmer, and place your double boiler overtop.

Step 14

Combine the sugar, lime juice, lime zest, and egg yolks in the double boiler, and whisk to dissolve the sugar. Continue stirring, constantly, until the temperature passes 140°F. This will ensure the egg yolks are properly cooked, and eliminate any chance of obtaining a food-borne illness. Then, continue stirring until the mixture starts to thicken, a few minutes more.

Step 15

In a small bowl, add the cold water and pour in the gelatin. Let it sit for a few minutes to "bloom."

Step 16

Remove the curd mixture from the heat and add in your butter and bloomed gelatin. Whisk everything together until the butter has melted and gelatin is fully dissolved.

Step 17

Let this curd cool to room temperature, first, and then in the refrigerator. It will continue to thicken as the temperature drops.

Step 18

Using a melon baller or cupcake corer, remove the centers of your cupcakes. Keep the scraps in a separate container - we don't waste any of the good stuff.

Step 19

Next, add the cooled and thickened curd to a piping bag. Fill each cored cupcake center with the curd.

Step 20

Then, press a scoop of cake back over the curd hole. These extra cake bits will likely bulge over the top of the rest of the cupcake, which is fine. When we pipe the buttercream, this extra domed shape will help add some pretty height to the icing.

Step 21

Add your softened butter and shortening to the bowl of your mixer and combine.

Step 22

Slowly add powdered sugar to the butter, one cup at a time, mixing and scraping down the bowl in between each new addition.

Step 23

To the buttercream, add in the lime juice and zest, as well as the vanilla. Mix well, and test the taste, adding more juice or vanilla if you'd prefer. This buttercream is best with a bright zing of key lime flavor, so don't hold back if you think it needs a bit more.

Step 24

Next, insert a star or rosette tip of your choosing into a piping bag, and fill it with your delicious buttercream. In a circular motion, apply buttercream to the cupcake, starting at the outer edge, moving up and in with steady pressure on the bag.

Step 25

Sprinkle on to the buttercream some extra lime zest for a zingy, finishing touch.

Step 26

Start off by setting a pan of water on the stove to boil.

Step 27

Cut the limes into thin slices, and then half or quarter each slice.

Step 28

Drop the lime slices into your pan of boiling water. Let them cook for two minutes. Then, strain them into a bowl of ice-cold water, reserving the boiling water. If you accidentally strain out the water, it's okay - you'll just have to reboil another pot. :)

Step 29

Stir the sugar back into the boiling water, and let it dissolve.

Step 30

Then, add your lime slices into the simmering sugar water. Let them cook for about 15 minutes, or until the piths (the white parts of the lime) are translucent.

Step 31

Remove the lime slices to a cooling rack. I suggest you place some tin foil underneath the rack for easy cleanup - these slices get very sticky as they dry!

Step 32

Once the lime slices are mostly dried, toss them in some sugar and let them set on a sheet of wax paper.

Step 33

Top each one of your cupcakes with a delicious candied lime slice and enjoy!