Make the cupcakes: Preheat oven to 350 °F. Place cupcake liners in a standard cupcake tin.
In a medium bowl, sift together flour, salt and baking powder. Stir well and set aside. In the bowl of an electric mixer, beat together sugar and eggs on medium speed for about one minute. Gently stir in oil, milk and vanilla into sugar and egg mixture. Gradually add dry ingredients to this mixture, and beat for one minute at medium speed.
Divide batter equally into two separate bowls. Add orange food coloring to one bowl of batter, and black food coloring to the other bowl of batter. Mix food coloring into each separate batch of batter until well blended. Using separate spoons for each color batter, layer orange batter and then black batter in each cupcake liner until they are 2/3 full. Dip a butter knife into each cup and gently swirl together once or twice, so the colors do not mix too much, but form a pattern in the cake batter. Bake for 20-22 minutes, or until a toothpick inserted into the center of one of the cupcakes comes out clean. Cool cupcakes on a rack for at least five minutes before removing from the pan. Allow them to cool completely
Make the buttercream: In a stand mixer fitted with the whisk attachment, mix the butter and confectioners’ sugar by starting the mixer on low speed. Continue on low speed and beat ingredients together until the mixture is crumbly. Increase speed to high and beat for 3 minutes. Add vanilla extract and beat together again for another minute until light and fluffy. If the buttercream is too stiff, add milk or heavy cream a tablespoon at a time until the mixture is of spreading consistency.
To make the swirl frosting effect, separate half the frosting into another mixing bowl and blend drops of orange food coloring. Add as much food coloring as you like until you get the desired color intensity (we used about 2 teaspoons). Repeat the process with the green food coloring with the remaining frosting left in the mixing bowl.
Lay one or two large sheets of plastic wrap on a work surface. Spoon the orange frosting onto the center of the plastic wrap in an oblong shape. Spoon the green frosting onto the plastic wrap right beside the orange so that the two frostings are touching and generally have the same oblong shape. Lift one edge of the plastic wrap and fold it over so that the orange frosting is sitting on top of the green frosting. Twist the ends of the plastic wrap together so that the two-tone frosting is held securely inside.
Fit a piping bag with a jumbo closed star tip (Ateco 856). Snip one end of the plastic wrap holding the frosting and gently guide the open end into the piping bag. Pipe the frosting onto the cooled cupcakes. Immediately add Halloween sprinkles. Garnish with Halloween picks, if desired.
Keyword buttercream swirl, confetti cupcakes, two tone icing