Preheat the oven to 350 degrees. Line 14 to 15 muffin cups with paper liners and set pans aside.

Place the butter in a large mixing bowl and beat with an electric mixer set to medium until very smooth. Beat in the sugar, vanilla, cinnamon, baking powder, baking soda, and salt and beat until well combined (mixture will be crumbly). Add the eggs one at a time, beating well after each addition.

With mixer on low, beat in half of the flour followed by half of the buttermilk and beat to combine. Add the remaining flour mixture, then the remaining buttermilk and beat until just incorporated.

Divide the batter between the prepared muffin cups, filling each two-thirds full. Bake 16 to 20 minutes, until a cake tester inserted into the center of the cupcakes comes out clean.

Remove cupcakes from the oven and cool completely on a wire rack before frosting them.

Place the butter in a medium mixing bowl and beat with an electric mixer until very smooth. Add 3 cups of the powdered sugar, 3 tablespoons of the milk, and the vanilla and salt.

Beat on low to combine, then turn mixer to medium and beat until frosting is smooth. Add add additional powdered sugar if frosting is too thin; if it’s too thick add additional milk.

Pipe or spread the frosting on the cupcakes. Sprinkle the granulated sugar and cinnamon over the frosted cupcakes and serve. Uneaten cupcakes can be stored (covered with plastic wrap) in the fridge for up to 2 days or in the freezer (tightly wrapped) for up to 3 months.