In a medium saucepan, over medium heat combine the brown sugar, butter and corn syrup.
Once they are melted, add the can of sweetened condensed milk and stir. Heat until it comes to 245 degrees F. Stir continuously with a wooden spoon. Be careful not to burn. Remove from heat and add the vanilla. Let cool slightly before dipping apples.
Line half sheet pans with parchment paper and spray lightly with cooking spray.
Place caramel dipped apples on half sheet pans lined with parchment paper. Let the caramel harden in a cool place. If desired, dip in melted chocolate or drizzle melted chocolate. While the chocolate is still wet, roll the apples in your desired toppings.
If you are doing a topping such as candy pieces (such as M&M's), let the chocolate harden slightly before pressing on the candy. Otherwise it will slide off.
Let the apples dry in a cool location.
Once caramel and/or chocolate is set, package in clear bags, add a twist tie and refrigerate or store in a very cool (but not freezing) location.