Preheat oven to 350 F and line cupcake pan with paper liners.
In medium bowl, combine flour, baking powder, cinnamon and salt.
Using electric or stand mixer, cream butter, sugar and brown sugar about 4 minutes on medium or medium-high speed until light and fluffy. Add egg, mixing well and scraping down bowl.
In small bowl or measuring cup, whisk milk and vanilla. Set aside.
Add 1/3 dry ingredient mixture to butter mixture and beat until combined. Add 1/2 milk mixture and mix well. Continue alternating dry and wet ingredients.
Bake about 16 minutes, or until toothpick inserted in middle of cupcake comes out clean. Cool in pan 5 minutes then transfer to wire rack to cool completely before frosting.
To make frosting: Using electric or stand mixer, beat butter and salt on medium-high speed 5 minutes, scraping down bowl halfway through.
Reduce speed to low and add sugar 1/2 cup at a time, alternating with heavy cream until 3 tablespoons have been added. Stop occasionally to scrape down bowl. Once all sugar is in, add vanilla and beat on medium-low 1 minute until light and fluffy. If desired, add additional cream 1 teaspoon at a time until frosting reaches preferred consistency.
Place buttercream in piping bag with large round tip. Pipe tall mounds of frosting on each cupcake in ghost shapes (wider on bottom, narrower on top). Add dots of black food dye or chocolate chips for eyes.
