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Special equipment: an 18-inch piping bag fitted with a star tip and a kitchen blowtorch
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For the cookie crumb mixture: Mix together the cookie crumbs and melted butter in a small bowl.
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For the cake batter: Preheat the oven to 375 degrees F. Line two 12-cup muffin pans with cupcake liners.
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Put 1 tablespoon of the cookie crumb mixture in the bottom of each cupcake liner.
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Set the muffin pans aside.
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In the bowl of a stand mixer with a paddle attachment, beat the butter on medium speed until light in color and fluffy, about 6 minutes.
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Add the sugar and continue beating until uniformly incorporated into the butter; stop the mixer and scrape down the sides of the bowl.
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Restart the mixer on low speed and add the eggs one at a time, waiting until each egg is fully incorporated before adding the next.
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Once the eggs have been added, stop the mixer and scrape down the sides of the bowl to insure that all of the ingredients are incorporated.
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Add the vanilla bean paste and blend uniformly.
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Add the gluten-free baking mix in three additions, alternating with the milk in two additions, fully incorporating each addition into the batter before moving to the next.
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If needed, stop the mixer after each addition, scrape down the sides of the bowl and resume mixing on low.
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Fill the cupcake liners two-thirds full with the batter and bake until the top of each cupcake is slightly springy to the touch and a toothpick inserted in the center comes out clean, 14 to 16 minutes.
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Immediately turn the cupcakes out of the pans onto a cooling rack and let cool completely.
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For the lime filling: In a small bowl, mix 1 tablespoon water with the lemon juice; sprinkle the gelatin over the liquid and let the gelatin bloom and hydrate.
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In the bowl of a stand mixer, whip the cream on high speed to medium-firm peaks.
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Melt the bloomed gelatin in the microwave just until melted and clear, 15 to 20 seconds; do not overheat as this will kill the gelatin!
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Stir the key lime curd into the gelatin until all mixed in, and then pour the lime curd into the whipping cream.
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Mix completely and refrigerate until ready to use.
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For the meringue frosting: In a small saucepot, combine the sugar and 1/3 cup water and set over high heat.
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With a wet pastry brush, wipe down any sugar crystals on the sides of the pot.
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Cook until the sugar mixture registers 280 degrees F on a candy thermometer.
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While the sugar syrup is cooking, beat the egg whites and cream of tartar in the bowl of a stand mixer with a whisk attachment on medium-high speed until the mixture reaches the medium-peak stage.
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Turn the mixer down to medium low and very, very, very slowly pour the hot sugar syrup into the whipping egg whites.
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Once all the sugar is added, add the vanilla bean paste and turn the speed up to high.
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Whip until the mixture is very light and fluffy and the mixing bowl is no longer hot to the touch, about 9 minutes.
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Fit an 18-inch piping bag with a star tip and twist and hold the bag right by the tip to prevent the frosting from leaking out.
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Fold the top of the piping bag over your hand and spoon the meringue frosting into the bag.
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To assemble, use an apple corer or paring knife to core out the center of each cupcake.
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Fill each cupcake with some of the lime filling and top with some of the meringue frosting.
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Use a blowtorch to lightly toast the top of the meringue.
