Line twenty-four to thirty 2 1/2-inch muffin cups with paper bake cups; set aside. Combine the first four ingredients (through salt.)
Preheat oven to 350 degrees F. In a large mixing bowl beat butter on medium for 30 seconds. Gradually add sugar, 1/4 cup at a time, beating on medium until combined. Scrape bowl; beat 2 minutes more. Add eggs, one at at time, beating after each. Beat in vanilla. Add flour and milk alternately, beating on low after each addition until well combined. Spoon batter into prepared cups, filling about 1/2 full. Combine 3 tablespoons sugar and 2 teaspoons cinnamon. Sprinkle half of the cinnamon-sugar mixture over the batter.
Bake 18 to 20 minutes or until a toothpick comes out clean. Cool cupcakes in pans for 5 minutes. Remove cupcakes from pans; cool on wire racks.
Spoon frosting into a large pastry bag fitted with a large star tip. Pipe frosting on cupcakes. Sprinkle with the remaining cinnamon-sugar mixture. If desired, garnish each cupcake with churro piece.
In a very large mixing bowl beat butter on medium until smooth. Gradually add 2 cups of the powdered sugar, beating well. Slowly beat in the 1/4 cup milk and 2 teaspoons vanilla. Gradually beat in remaining powdered sugar and cinnamon until smooth.