For the Cupcakes:
1½ cups all-purpose flour
1½ cups cake flour
1 tablespoon baking powder
½ teaspoon salt
1 tablespoon ground cinnamon
1 cup unsalted butter, at room temperature
1¾ cups granulated sugar
4 eggs, at room temperature
2 teaspoons vanilla extract
1¼ cups whole milk
For the Seven-Minute Frosting:
1½ cups plus 2 tablespoons granulated sugar, divided
2/3 cup water
2 tablespoons light corn syrup
6 egg whites, at room temperature
For the Garnish:
2 tablespoons granulated sugar
½ teaspoon ground cinnamon
1. Preheat oven to 350 degrees F. Line standard muffin tins with paper liners. Sift together both flours, baking powder, salt and cinnamon.
2. With an electric mixer on medium-high speed, cream the butter and sugar until pale and fluffy, about 3 minutes. Add the eggs, one at a time, beating until each is incorporated, scraping down the sides of the bowl as needed. Beat in the vanilla. Reduce the speed to low. Add the flour mixture in three batches, alternating with two additions of milk, and beating until combined after each.
3. Divide the batter evenly among lined cups, filling each three-quarters full. Bake, rotating tins halfway through, until a cake tester inserted in centers comes out clean, about 20 minutes. Transfer tins to wire racks to cool completely before removing cupcakes and frosting. Cupcakes can be stored up to 2 days at room temperature, or frozen up to 2 months, in airtight containers.
4. Make the Frosting: Combine 1½ cups granulated sugar with the water and corn syrup in a small saucepan. Bring to a boil over medium heat, stirring occasionally, until sugar dissolves. Continue boiling, without stirring, until syrup reaches 230 degrees F.
5. Meanwhile, in the bowl of a standing electric mixer fitted with the whisk attachment, whisk egg whites on medium-high speed until soft peaks form. With mixer running, add remaining 2 tablespoons granulated sugar, beating to combine.
6. As soon as sugar syrup reaches 230 degrees F, remove from the heat. With the mixer on medium-low speed, pour syrup down the side of the bowl in a slow, steady stream. Raise the speed to medium-high; whisk until the mixture is completely cool (test by touching the bottom of the bowl) and stiff (but not dry) peaks form, about 7 minutes. Use immediately.
7. Using a pastry bag fitted with a large plain tip (Ateco #809 or Wilton #1A), pipe frosting on each cupcake: Hold the bag over the cupcake with tip just above the top, and squeeze to create a dome of frosting, then release pressure and pull up to form a peak.
8. Combine the 2 tablespoons granulated sugar and ½ teaspoon cinnamon. Using a small, fine sieve, dust the peaks with cinnamon-sugar. Frosted cupcakes are best eaten the day they are frosted; keep at room temperature until ready to serve.