Preheat oven to 350 degrees. Line standard muffin tins with paper liners. Sift together both flours, baking powder, salt, and 1 tablespoon cinnamon.
With an electric mixer on medium-high speed, cream butter and sugar until pale and fluffy. Add eggs, one at a time, beating until each is incorporated, scraping down sides of bowl as needed. Beat in vanilla. Reduce speed to low. Add flour mixture in three batches, alternating with two additions of milk, and beating until combined after each.
Divide 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. Cupcakes can be stored up to 2 days at room temperature, or frozen up to 2 months, in airtight containers.
In standing mixer fitted with whisk attachment, beat butter at medium-high speed until smooth, about 20 seconds. Add confectioners’ sugar and salt; beat at medium-low speed until most of the sugar is moistened, about 45 seconds. Scrape down bowl and beat at medium speed until mixture is fully combined, about 15 seconds; scrape bowl, add vanilla, cinnamon, and heavy cream, and beat at medium speed until incorporated, about 10 seconds, then increase speed to medium-high and beat until light and fluffy, about 4 minutes, scraping down bowl once or twice.