Wash and scrub the apples thoroughly to remove wax and residue. Dry them completely, remove the stems, and insert a wooden stick into the stem end of each apple.

Line a baking sheet with parchment paper or a silicone baking mat, then lightly grease it. Chill the prepared apples while the caramel cooks if desired.

Combine the brown sugar, corn syrup, butter, sweetened condensed milk, and salt in a heavy-bottomed saucepan. Cook over medium heat, stirring frequently, until the butter melts and the mixture reaches a gentle boil.

Continue cooking and stirring until a candy thermometer reads 235–240°F, or 113–116°C. This usually takes 10–15 minutes after boiling begins and indicates the soft-ball stage.

Remove the saucepan from the heat and stir in the vanilla extract. Let the caramel cool for about 5 minutes so it thickens slightly while remaining fluid enough for dipping.

Dip each apple into the warm caramel and turn it slowly to coat the fruit. Hold it above the pan for a moment so excess caramel can drip back into the saucepan.

Place the dipped apples stick-side up on the prepared baking sheet. Add chopped nuts, sprinkles, crushed cookies, or flaky sea salt immediately while the coating is still sticky.

Let the caramel apples set at room temperature for 30–60 minutes, or refrigerate them briefly for faster setting. Serve once the coating is firm enough to handle.