9. Make the Meringue Syrup
While the pie chills, make the topping. Fill a large saucepan with 1 to 2 inches of water. Place over medium-low heat and bring the water to a simmer. Meanwhile, whisk together the remaining 100 grams (½ cup) sugar with the egg whites, cream of tartar, and salt in a heat-proof bowl that will nestle inside the saucepan without touching the water. Place the bowl in the saucepan and cook the egg mixture, whisking gently, until the mixture reaches 165°F (74°C), 2 to 5 minutes.