Remove stems from apples and insert stick into the stem of each apple. Refrigerate on baking sheet.
In a 12 cup heavy bottomed saucepan, melt together granulated and brown sugars, butter, condensed milk, corn syrup and salt, stirring. Bring to a boil over medium-high heat, stirring and making sure to stir around bottom edge of pot to prevent caramel from scorching.
Reduce heat to medium-low; boil, stirring often, for 18-20 minutes (or until thickened), deep caramel color (234-236 degree F, 112-113 degree Celsius on a candy thermometer). Remove from heat. Stir in vanilla. Let cool for 5 minutes.
Line rimmed baking sheet with greased foil. Holding apple by the stick, swirl all but the top of each apple in caramel, allowing excess to drip back into saucepan (if you are rolling the apples in nuts etc. this is the time), place on prepared baking sheet; refrigerate until caramel is set, about 15 minutes.