Put apples into a saucepan with the butter. Cover and simmer about 20 minutes. Add ½cup sugar and ¼teaspoon salt. Cook until thick and dry. Remove from heat. Pour into a food mill and let juice and butter drain from the apples. Discard liquids. Grind through the food mill and into a bowl. Add vanilla and mix. Preheat oven to 310 degrees.
Put ¼cup sugar and water into a 6-cup charlotte mold, or an enameled soufflé dish. Boil in the pan and caramelize the sugar. When dark brown, lift from heat and twist pan around to coat sides. Set pan into cold water to harden the caramel.
Add yolks to apples and mix well. Add ¼teaspoon salt to whites in mixer bowl and beat until they start to stiffen. Gradually add ¼cup of sugar and beat until creamy and stiff. Fold into the apples. Pour into caramelized mold, filling it ¾ full.
Set mold into a hot water bath. Bake 1¼ hours. When mold is done, remove from oven, set on a cake rack, and cool for 30 minutes. Mold will settle as it cools.
To serve, run knife around top and then down to the bottom of the mold. Place serving dish over top and invert. Surround with sauce and serve. Make the cream sauce while the soufflé bakes.