Mix together: sugar, cornstarch, and salt. Add to milk. Cook until thick and smooth, about 15 minutes. Add a small amount of mixture to the yolks. Combine yolks with mixture, and cook for a few minutes. Remove from heat, and add gelatin and butter. Cool completely, then add vanilla. Whip cream, then fold into mixture. Pour all into a prebaked crust, sprinkle with nutmeg, and chill until firm.