Preheat oven to 375 degrees on a convection oven and 400 degrees on a conventional oven. Brush six 7-ounce 3 3/4-by-1 3/4-inch ramekins generously with butter; coat with granulated sugar. Place on a rimmed baking sheet.
In a small bowl, whisk together sugar and egg-white powder; set aside. In the bowl of an electric mixer fitted with the whisk attachment, whisk whites on low speed until frothy, about 2 minutes; whisk in sugar mixture. Increase speed to medium and beat until soft peaks form, about 5 minutes.
Meanwhile, set chocolate in a large bowl. In a small saucepan, whisk milk, cornstarch, and salt to combine. Bring to a simmer, whisking; remove from heat. Whisk into chocolate (mixture will separate). Vigorously whisk in yolks and 3 tablespoons creme fraiche until smooth. Gently whisk in one-third of the egg white mixture. Using a rubber spatula, fold in remaining egg whites.
Fill ramekins evenly with batter, almost to the top. Transfer to oven and bake for 10 minutes for gooey souffles or 12 to 13 minutes for firmer souffles, rotating baking sheets halfway through baking.
Meanwhile, in a small bowl, whisk together remaining 1/2 cup creme fraiche and confectioners' sugar until soft peaks form. Make a hole in the center of each souffle; fill each with a tablespoon sweetened creme fraiche. Serve immediately.