In a medium heavy saucepan over medium-high heat, bring sparkling cider to a boil. Continue boiling and stirring until reduced to 1 cup, about 15 minutes. Remove from heat; chill in the refrigerator to cool completely.*

In a mixing bowl, whisk together the flour, baking powder, baking soda, and salt until combined; set aside.

In the bowl of a stand mixer fitted with a paddle attachment, beat the butter and sugar together on medium speed until lightened and creamy. Beat in the eggs, one at a time, until combined, scraping down the sides and bottom of the bowl as needed. Beat in the Greek yogurt, sparkling cider reduction, and vanilla on medium speed.

Pour half of the dry ingredients into the wet ingredients and mix until combined. Add the remaining dry ingredients, then mix until just combined, scraping down the sides and bottom of the bowl as needed.

Fill cupcake liners 2/3 of the way full. Bake for 18-20 minutes or until a toothpick inserted in the center comes out clean or with few crumbs attached. Allow to cool in the pan for 5 minutes before transferring to a wire rack to cool completely.

In the bowl of a stand mixer fitted with a paddle attachment, beat the butter and shortening together until smooth and creamy. Add 2 cups of powdered sugar and beat until smooth.

Add the sparkling cider reduction, starting with 6 Tablespoons, along with the remaining 2 cups of powdered sugar, and beat until combined. Add more of the cider reduction, if needed to get the right consistency.

Frost or pipe buttercream onto cupcakes, as desired. Garnish with sprinkles. Cupcakes keep well covered tightly at room temperature or in the refrigerator for up to 5 days.