Insert wooden skewers or sticks into the top of each apple, creating a handle for dipping. Place the apples on a prepared baking sheet lined with parchment paper and set aside.
Combine sugar, corn syrup, and water in a medium saucepan. Stir gently over medium heat until the sugar dissolves completely and the mixture begins to boil.
Insert a candy thermometer and cook the mixture until it reaches 300°F (hard crack stage), watching for the color to turn a deep amber. Add a few drops of red food coloring and stir quickly to evenly distribute, creating a dark, sinister hue.
Once the toffee reaches the correct temperature and color, remove it from the heat immediately to prevent burning. Be cautious—the mixture will be extremely hot and bubbly.
Dip each apple into the hot toffee, twisting gently to coat the entire surface evenly. Let excess toffee drip back into the pan for a few seconds.
Place the coated apple on the parchment-lined sheet and allow the toffee to cool and harden completely—about 10-15 minutes. Repeat with remaining apples.
Once cooled, check that the toffee is firm and glossy. Your Poison Toffee Apples are ready to serve or decorate further for a spooky effect.
