Preheat oven to 200°F/90°C. Line a baking sheet with parchment paper and set aside. Make sure that you have your piping bag ready to go and painted with your food coloring if using.
Be sure that your mixer bowl is clean and has no traces of grease, any residue can result in the whites not coming together. Be sure your whisk and bowl are spotlessly clean! In a bowl of an electric mixer fitted with the whisk attachment, whisk egg whites, cream of tartar, and salt on low-medium speed until foamy and soft peaks start to form, approximately 40-50 seconds.
Then, while mixer is running, add the sugar, one tablespoon at a time, and continue whisking on medium-high speed until stiff peaks form, meringue is glossy and smooth but not dry, making sure that the sugar is fully dissolved (this process of adding the sugar and beating may take 5-10 minutes). Stop the mixer and remove the bowl.
Fold in the coulis or jam if using.
Immediately load your piping bag and pipe meringue cookies onto your parchment-lined baking sheet. They don't spread much, so you can place them relatively close. Bake in the lower part of the oven for 1 hour or until the meringues are dry, lift easily from the parchment paper and their centers aren't gummy. Turn off the oven and, without removing, let meringues cool completely for at least one hour or overnight.