Make the Cupcakes
Line 24 muffin cups with paper back cups
In a medium bowl stir together flour, baking powder, and salt.
In a medium bowl stir together brown sugar and cinnamon. Set aside.
Preheat oven to 350 degrees.
In a large mixing bowl of an electric mixer, add the butter and beat on medium to high speed for 30 seconds.
Gradually add granulated sugar, about ¼ cup at the time, beating on medium speed until combined, scraping sides of bowl occasionally.
Beat on medium speed about 2 minutes more or until light and fluffy.
Add eggs, one at a time, beating well after each addition until combined.
Beat in vanilla.
Alternately add flour mixture and milk to butter mixture, beating on low speed after each addition just until combined (batter may look curdled but at the end it will blend well).
Spoon about 1 tablespoon of the batter into each prepared muffin cup. Sprinkle about 1 teaspoon of the brown sugar mixture over batter in cups.
Spoon the remaining batter evenly over brown sugar mixture in cups. Sprinkle the remaining brown sugar mixture over batter in cups.
Bake for 15 to 18 minutes (mine took 15 minutes), or until a toothpick inserted in centers comes out clean.
Cool cupcakes in muffing cups on wire racks for 10 minutes. Remove cupcakes from muffin cups and cool completely on wire racks.
Make the Frosting
In a large mixing bowl beat butter with an electric mixer on medium to high speed for 30 seconds.
Beat in 1 teaspoon vanilla and a dash of salt.
Gradually add 4 cups powdered sugar, beating until combined.
Beat in ¼ cup whipping cream.
Beat in 4 cups additional powdered sugar. Beat in 2 to 3 tablespoons additional whipping cream until frosting is light and fluffily and reaches spreading (or piping) consistency.
Makes 4 cups.