In a medium saucepan or heavy-bottom pot, 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. Use a candy thermometer to monitor the temperature.
Stir continuously with a high-heat or wooden spoon. Be careful not to burn.
Remove from heat, add the vanilla and stir to combine. Let cool slightly before dipping apples.
Keep the pot of caramel over the lowest heat setting while dipping the apples. If the caramel isn’t kept warm, it will cool down and become too thick by the time you finish dipping all the apples, making them more difficult to coat evenly.
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 rolling into toppings, do this right away before placing onto prepared sheet pans.
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.