In a medium-sized saucepan (I used a 2-quart pan
), stir together the erythritol, agave, water, and salt, until evenly mixed. Place over medium-high heat and add a candy thermometer to the pot. Cook without stirring until it reaches 220 degrees Fahrenheit. While this is on the stove, put the egg whites in stand mixer bowl with whisk attachment. When the stovetop mixture reaches 260 degrees, start beating the egg whites on medium/high until stiff peaks form. When the temperature reaches 280 degrees, remove the pan from the heat.