Preheat oven to 200 degrees F and line a baking sheet with parchment paper. Set aside.
Pour egg whites in a large bowl and using an electric mixer, start beating it on low.
Add cream of tartare.
Slowly add sugar and gradually increase mixer to its highest speed.
Continue mixing until mixture turns bright white and forms semi-stiff peaks.
Scoop meringue mixture into a piping bag with Wilton tip #12 attached.
Pipe out meringue mounds on lined baking sheet – to do so, create a base about 1 inch in diameter and continue piping until it’s about 2 inches high, pulling and quickly releasing your grip on the icing bag to create a pointed tip.
Bake for 2 hours. Once time is up, turn off the heat on the oven and leave inside for an additional 30 minutes.
As the meringue bakes, prepare your buttercream frosting – to start, add butter, confectioners’ sugar and milk into a large bowl.
Use an electric mixer to beat together all ingredients.
Once everything is well-incorporated and smooth, add one small drop of violet gel food coloring. Continue to mix until the buttercream is completely tinted purple.
Scoop out the buttercream into a piping bag with Wilton tip #12 attached. Frost each cupcake.
Remove meringue from oven and allow to cool for a few minutes.
Attach Wilton tip #3 on black decorating frosting and pipe out eyes and mouth on each meringue cookie.
Place one meringue ghost on each cupcake. If there are any extras, serve alongside the cupcakes.