With an electric hand mixer, whip egg whites on low speed, increasing to medium speed until the egg whites begin to froth. (This can also be made in the large bowl of a stand mixer with the whisk attachment.)

Next, mix on high until white and foamy.

Add cream of tartar and half of the sugar. Continue to whip until egg whites begin to thicken and soft peaks form.

Add remaining sugar and vanilla and continue whipping on high several minutes until stiff peaks form.

Add a drop of green food coloring and mix until well incorporated.

Place the meringue mixture in a large piping bag fitted with a large star tip or closed star tip.

Pipe meringue onto the prepared baking sheet using a circular motion to create a small Christmas tree shape.

Add a star shaped sprinkle to the top of the tree, then add additional sprinkles to decorate the trees.

Place in the oven and bake for 2 hours. When finished baking, turn the oven off and open it slightly. Leave the meringue Christmas cookies in the oven while they cool (about 1 hour).