Preheat the oven to 225F. Line a large baking sheet with a silicone baking mat or parchment paper and set it aside. Fit a disposable piping bag with either a rounded or a star tip and set that aside.
In a large bowl (make sure it is completely clean and dry) place the egg whites, cream of tartar and salt. Use either a hand mixer or a stand mixer fitted with a whisk attachment and beat the egg white mixture on high speed for about 3 minutes or so, until soft peaks form. Then while the mixer is still running, gradually add in the sugar and continue to beat on high speed until stiff peaks form, about 2 or so more minutes. If using the food coloring, beat it in now.
Use a rubber spatula to transfer the egg white mixture into the prepared piping bag.
Pipe out mounds onto the prepared baking tray, raising them up as you do. They won't spread, so you can place them fairly close together. If using sprinkles, then sprinkle them over the meringue cookies now.
Bake for 60 minutes, then turn the oven off but leave them in the oven for another hour or so. After that, take the tray out of the oven and let them come completely to room temperature. Serve immediately after.
These can be stored covered at room temperature for up to 2 weeks.
