Preheat the oven to 350 degrees F. Thoroughly butter 4 souffle ramekins with a pastry brush and set aside. Combine the skim milk and whipping cream in a saucepan and heat to just before boiling with constant stirring; remove from the stove. In a bowl, whisk the egg yolks and 1/4 cup granulated white sugar for 2 minutes, continue mixing until the egg yolks turn a light golden yellow color. Add the cornstarch to the egg yolks and continue whisking; they should thicken slightly. Whisk a few tablespoons of the heated skim milk and whipped cream into the egg yolks. Slowly add the remaining heated skim milk and whipping cream to temper the egg yolks; whisk for 1 minute. Return the entire custard mixture to the saucepan and heat gently; whisk the entire time until it thickens, continue to cook at a low heat, 3 to 4 minutes total cooking time; do not boil. Remove the cooked custard base from the heat. Place the egg whites in a glass, stainless steel or copper bowl; mix with beaters on medium speed for 1 minute (use a timer). At the 1 minute mark, gradually add the remaining 1/3 cup granulated white sugar; continue to mix for 1 minute. Add the lemon juice to the whipped egg whites and continue to beat for 1 additional minute, for a grand total of 3 minutes of whipping. Transfer the custard base to a large glass or stainless steel bowl and add the vanilla extract; combine thoroughly. Add half of the whipped egg whites to the custard base, whisk together forcefully until a smooth uniform mixture. Gently fold the remaining half of the whipped egg whites into the custard base. Fill the buttered ramekins with the souffle batter, ensuring that no large air pockets are formed. Level the souffle batter in the ramekin and run a thumb around the edge to create a small ridge. Place the souffles in a 2-inch deep oven-safe dish and fill with room temperature water to approximately one-third the height of the ramekins. Bake the souffles for 20 minutes. Turn the oven off and let the souffles rest for 5 minutes with the oven door closed. Remove the souffles from the oven, garnish with a dusting of icing sugar and serve immediately.