Heat oven to 275F. Place oven racks in upper and lower third of oven. Line 2 large baking sheets with parchment.
In the bowl of a stand mixer, using the whisk attachment, beat egg whites, cream of tartar, and vanilla on high speed until foamy. Beat in the sugar, 1 tablespoon at a time; continue beating until stiff, glossy peaks form and sugar is almost dissolved, 5 to 6 minutes, scraping the sides of the bowl occasionally. DO NOT UNDERBEAT.
Sprinkle the cocoa through a fine mesh strainer over the top of the meringue; fold the cocoa into the mixture.
Fill a piping bag with the meringue and pipe into 2-inch circles. Repeat until you have used all the meringue.
Wet your thumb or forefinger and make a slight dip or crater in the top of the meringues. This is where you’ll drizzle the caramel after the meringues have baked.
Place both cookie sheets in the oven. Bake 30 minutes. Turn the oven off, but do no open the door. Leave the meringues in the oven with the door closed for 1 hour.
Remove from the oven and place the pans on cooling racks to cool at room temperature for about 2 hours.
Spoon a dollop of cooled caramel into the center crater and sprinkle with salt. Let stand about 1 hour for the caramel to thicken in meringue.
To make the Caramel
Place the sugar in a saucepan and give it a little shake so that the sugar lays flat in an even layer. Add the water.
Turn the heat to medium and cook (do not stir) until the sugar dissolves into a clear syrup. It will look cloudy at first, but will eventually give way to a clear, bubbling liquid.
Continue to cook until the caramel takes on an amber color. Do not leave the caramel’s side! Have the heavy cream standing by.
Once the caramel has gotten a golden, honey like color, turn off the heat and immediately add the cream. Add the butter. Stir until the caramel has an even texture.
The caramel will look very thin, but it thickens as it continues to cool. Refrigerate until ready to use, however, the caramel has the best drizzling consistency at room temperature.
