Remove apple stems, rinse the apples under very hot water for a few seconds, then scrub dry with a paper towel to help remove the wax around the apple. If possible, place the apples in the refrigerator for several hours or days in advance so they are well chilled before dipping.

Add butter, sugar, and karo syrup to a large heavy-bottom saucepan over medium heat. Stir over medium heat until mixture begins to boil, (about 5-10 minutes).

Gradually add the evaporated milk, a little at a time, stirring constantly, making sure it maintains a boil. Attach a candy thermometer and cook until it reaches 235 to 240 degrees F. (about 20-30 minutes).

Remove from heat and stir in vanilla. Pour into a heat-proof bowl for dipping.

Let caramel cool to 200 degrees while preparing apples.

Dry apples thoroughly with paper towels and insert craft sticks. Line a baking sheet with parchment paper.

Once caramel has cooled, dip apples and let excess drip off. Place on parchment-lined pan.