Preheat the oven to 100C/210F/gas mark ¼ and line two baking sheets with baking parchment.
Place the egg whites and cream of tartar in a large, spotlessly clean bowl and whisk on medium speed until soft peaks form. Gradually whisk in the sugar a couple of spoonfuls at a time until it is all incorporated; continue to whisk until the meringue is glossy and forms stiff peaks.
Spoon the meringue into a disposable piping bag and snip off the corner. Use a little of the meringue to stick the baking parchment to the tray so that it is easier to pipe.
Pipe bone shapes on one of the baking trays – start by piping a blob then work your way down to make the length, then finish with another blob on the opposite side. Repeat in reverse to make a crisscross, overlapping your meringue down the length of the bone to ensure there are no thin spots. It may take a few attempts to get the technique right.
Pipe ghosts on the other tray - start with a fat blob and tail off towards the top. Use a toothpick with a blob of meringue on the end to form arms.
Bake for about 1 hour until firm and the meringues lift away from the parchment cleanly. Remove from the oven and allow to cool.
Once cool, use a fine, food-only paintbrush to paint faces on the ghosts then store in an airtight container.