Wipe down the mixer bowl and whisk attachment with vinegar to remove any grease, wipe dry with a clean paper towel.

Add the cream of tartar and room temperature egg whites in the bowl of a stand mixer fitted with the whisk attachment. Turn the mixer on low to mix in the cream of tartar.

Slowly increase the speed to medium and beat until the mixture is foamy. Then increase the speed to high and beat until it holds soft peaks.

With the mixer running, slowly add the sugar, one tablespoon at a time, beating well between each addition.

Beat until it holds stiff peaks and it’s glossy. Add the vanilla and beat for 30 seconds.

Cut the tip off of a disposable pastry bag and fit it with a one-inch tip (you can also use bigger or smaller tips). Fill the pastry bag with the meringue.

Pipe the boos onto the prepared sheets. Make sure the bottom is wider than the top and pull up while you stop squeezing the piping bag to make a little point. You can put them close together because they don’t spread very much.

Add eyes to the boos (they don’t have to be perfect, they’re more fun if you make them silly).

Bake the trays for 60 minutes, rotating them halfway through. If you bake in the lower portion of the oven you won’t get browned ghosts.

Once they’re baked, turn off the oven and leave them in the oven for 60 minutes. Remove them from the oven and let cool completely.

Once they’re cool, use the gel frosting to add a mouth as desired.