Line a baking sheet with parchment paper.
Dip apples in boiling water for about 3 to 5 seconds. Gently wipe down the surface with paper towels to remove any wax residue on the skin. Pat dry.
Insert a wooden stick into the center of each apple through the stem end. Make sure apples are at room temperature.
Remove caramel from heat and add vanilla extract, stirring to combine.
In a saucepan over medium-high heat, combine butter, brown sugar, corn syrup, and condensed milk. Bring to a boil, stirring constantly. Lower heat to medium and continue to cook, stirring constantly for about 25 to 30 minutes or until a candy thermometer reads 248 degrees F. The caramel should coat back of a spoon. Check by dropping a teaspoon of the syrup into a glass of cold water. It's ready if it forms into a firm ball.
Quickly dip each apple into the hot caramel, swirling apples in the sauce to completely to about 1/2 inch of the wooden handle. Allow excess caramel to drip back into the pan.
Immediately (while the caramel is still hot) roll apples on peanuts to fully coat. Sprinkle peanuts on missed spots. Arrange apples stick side up on prepared baking sheet. Allow to completely cool.