Start by washing each apple thoroughly in warm water to remove the waxy coating that store-bought apples often have. Dry them completely with a clean towel, since any leftover moisture will stop the caramel from sticking properly. Once dry, push a wooden stick firmly into the top of each apple where the stem was.
Add your unwrapped caramel candies to a saucepan over low heat, stirring constantly so nothing scorches on the bottom. Once the caramels begin to melt, stir in the sweetened condensed milk to loosen the texture. Keep stirring until the mixture is completely smooth and pourable.
Holding each apple by its stick, dip it into the warm caramel and twist it slowly to coat the entire surface. Let any extra caramel drip back into the pan before setting the apple stick-side up on your prepared baking sheet. Place the tray in the fridge for about 15 minutes so the caramel firms up completely.
Once the caramel has set, melt your white chocolate candy melts in the microwave in 30-second bursts, stirring between each one. Add the vegetable oil to help thin the chocolate out so it coats more smoothly. Dip each chilled apple into the white chocolate, turning it to cover the caramel completely.
Set the finished apples back on the parchment-lined tray and immediately sprinkle on cinnamon sugar if you're using it, since the chocolate needs to still be wet for it to stick. Refrigerate the apples for another 20 to 30 minutes until the white chocolate is fully set. Once firm, they're ready to serve.