For the cake batter: Preheat the oven to 375 degrees F. Line two 12-cup muffin pans with cupcake liners and set aside.
In the bowl of a stand mixer with a paddle attachment, beat the butter on medium speed until light in color and fluffy. Add the sugar and continue beating until uniformly incorporated into the butter; stop the mixer and scrape down the sides of the bowl.
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. Once all the eggs have been added, stop the mixer and scrape down the sides of the bowl to insure that all the ingredients are incorporated.
Add the vanilla bean paste and orange zest and blend uniformly. Add the gluten-free baking mix in three additions, alternating with the milk in two additions, fully incorporating each addition before moving to the next. If needed, stop the mixer after each addition, scrape down the sides of the bowl and resume mixing on low.
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. Immediately turn the cupcakes out of the pans onto a cooling rack and let cool completely.
For the orange mousse filling: In a saucepot, gently heat 1/2 cup of the orange juice concentrate and the sugar, stirring just until the sugar is dissolved. Refrigerate until chilled.
In a small bowl, mix 2 tablespoons water with the remaining 1 tablespoon orange juice concentrate; sprinkle the gelatin over the liquid and let the gelatin bloom and hydrate.
In the bowl of a stand mixer, whip the cream on high speed to medium-firm peaks.
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! Stir the gelatin into the chilled orange juice mixture until combined, and then pour the orange juice mixture into the whipped cream. Mix completely and refrigerate until ready to use.
For the strawberry passion fruit Italian meringue buttercream: Put the sugar and 1/3 cup water in a heavy saucepan and heat over high heat until the sugar mixture registers 250 degrees F on a candy thermometer, 15 to 20 minutes.
While the sugar is cooking, whip the egg whites on medium speed in the bowl of a stand mixer to the soft-peak stage (the whites will look foamy and white), being careful not to over-whip. (If the whites start to look clumpy, they've been over-whipped. If this happens, toss them out and start again. If the whites are beating faster than the sugar is cooking, turn down the mixer speed. You can always turn up the speed if you need to.) Add the cream of tartar and continue whipping.
While the egg whites are whipping on medium speed, gently pour the sugar syrup down the side of the mixing bowl. Turn the speed up to high and whip until the mixing bowl no longer feels warm to the touch, about 7 minutes. Turn the mixer speed back to medium, add the butter in small chunks and mix until completely incorporated. Stop the mixer, scrape down the sides of the bowl and add the strawberry and passion fruit purees. Turn the mixer back to medium-low speed and mix until the purees have been incorporated.
Fit an 18-inch piping bag with a round tip and twist and hold the bag right by the tip to prevent the buttercream from leaking out. Fold the top of the piping bag over your hand and spoon the buttercream into the bag.
To assemble: Use an apple corer or knife to core out the center of each cupcake. Fill each cupcake with some of the orange mousse filling, and frost the top of each with some of the strawberry passion fruit Italian meringue buttercream.
This recipe was created by a contestant during a cooking competition. It has not been tested for home use.