Beat egg whites with cream of tartar and salt in a bowl with an electric mixer until foamy.

Gradually add sugar, a few tablespoons at a time, beating until dissolved before adding more. Continue beating until glossy and stiff peaks form; add vanilla extract.

Spoon meringue into a pastry bag fitted with a small tip.

Pipe meringue into bone shapes on prepared foil. Pipe all shapes at once to prevent deflation.

Bake for 1 hour without peeking. Turn off the oven and let cool inside for 1 hour.

Gently remove cookies from aluminum foil to avoid breaking.