Preheat oven to 350ºF, and line a muffin pan with cupcake liners. Add the Apple Cider mix to the hot water, and stir until fully dissolved; set aside.

In a large mixing bowl, whisk together the flour, baking soda, salt, spices, and both sugars until well blended. Add the yogurt, oil, applesauce, egg, vanilla, and cider liquid and stir until just combined.

Pour batter into cupcake liners, filling 2/3 of the way. Bake in the oven for 16-18 minutes, or until a toothpick inserted in the center comes out with few crumbs attached. Allow cupcakes to cool in the pan for 5 minutes before transferring to a wire rack to cool completely.

In a metal bowl of a stand mixer fitted with the whisk attachment, whisk the egg whites and sugar together. Remove bowl from mixer, then place over a pan of simmering water, not touching the water. Whisk until warm and sugar is dissolved, about 2-3 minutes. Mixture should feel completely smooth with no graininess when a bit is rubbed between two fingers. Remove from heat.

Return bowl to the stand mixer, and whip on high using the whisk attachment until mixture is thick and glossy, forming stiff peaks, about 4-5 minutes. Continue to whip until the bowl feels room temperature to the touch, about 3-4 additional minutes.

Switch the whisk attachment to the paddle attachment. With the mixer on low, drop in butter, 1 tablespoon at a time, beating well after each addition. If frosting appears curdled or clumpy at any time, increase speed to medium-high and beat until smooth. (See tips on curdled or runny buttercream above.)* Add the caramel and vanilla and beat until fully incorporated.

Frost or pipe buttercream onto cooled cupcakes, as desired. Drizzle with extra caramel syrup just before serving.