Thread each apple wedge onto a lollipop stick. Pat apple wedges dry with paper towel; arrange on parchment paper-lined baking sheet. Place peanuts in shallow bowl or pie plate. Set aside.
In large heavy-bottomed saucepan, combine sugar, ⅓ cup (75 mL) water, corn syrup, vinegar and salt. Bring to boil over medium heat, stirring until sugar is dissolved. Continue to boil, without stirring, and occasionally brushing insides of saucepan with pastry brush dipped in cold water (to prevent sugar from crystallizing on sides of saucepan), 10 to 12 min., or until candy thermometer registers hard crack stage (300°F/150°C to 310°F/154°C).
Remove from heat and immediately stir in butter and baking soda with wooden spoon; working carefully as hot mixture will bubble up.
Working quickly, dip apple wedges in candy, allowing excess to drip back into saucepan. Holding by the stick, roll each piece of candied apple in the peanuts; place on parchment paper-lined baking sheet. If candy hardens while dipping, place back on low heat and gently stir with wooden spoon until re-softened. Cool dipped apples until candy hardens.
When making hard candy, humidity may affect caramelization process, so avoid making on humid or rainy days.