Melt butter in a medium-sized, heavy-bottomed saucepan on medium-low heat.
Add brown and white sugar and corn syrup. Stir regularly, being sure to scrape the bottom of the pot, until the mixture begins to boil (about 30 minutes). Resist the temptation to raise the heat.
Add the sweetened condensed milk and continue to stir until the temperature on a candy thermometer reads 241 F. You can let it go all the way up to 248 F if you prefer the caramel to be really hard. I like mine to be solid enough to stick to the apple, but still soft enough to not break my jaw.
Remove from the heat and let the caramel cool for a couple of minutes.
While the caramel is cooling, wash and dry the apples and insert sticks.
Roll prepared apples into hot caramel and place into extra large baking cups or onto parchment paper.
Let cool for a couple of minutes and then decorate to your taste!
When you add the brown and white sugar, you can also add spices. I like to add pumpkin pie spice.While they are still warm, you can roll the coated caramel apples in: