Preheat oven to 200 F (93 C). Cover several baking sheets with parchment paper.
In an electric stand mixer fitted with the whisk attachment, add the egg whites, cream of tartar and salt. Make sure the bowl and whisk are freshly cleaned and dried. Whisk on medium until the eggs are frothy and then slowly add in C&H® Granulated Sugar, 1 tablespoon at a time. Really take your time here so that the sugar has time to dissolve; this should take about 5 minutes. When all of the sugar is in, turn the mixer on high and just before you reach stiff peaks, dump in the C&H® Confectioners’ Sugar. Run the mixer on low to combine and then increase to high until you reach stiff peaks again, which should take less than a minute depending on the speed of your mixer. The meringue will look glossy and hold its shape when you invert the whisk. The tip of the inverted meringue will be just shy of 12 o’clock. It should also feel smooth when you rub some between your fingers.
Divide the meringue into 6 mounds on the prepared baking sheet(s). Leave 1- to 2-inches of space between each meringue so that the heat can evenly circulate around them in the oven.
Bake in the center of the oven for 2 hours. Check at some point between 1 and 1 1⁄2 hours to make sure the meringues aren’t browning and are still white. If they’re browning, turn off the oven. Let the meringues cool completely inside the oven. This should take several hours.