10 popsicle sticks or chopsticks and a candy thermometer
Rinse and dry the apples. Spray a baking sheet with cooking spray. Push one stick into the top of each apple, then place on the baking sheet with the stick standing straight up.
Place the cookies in a large resealable plastic bag and roll with a rolling pin to crush. Set aside.
In a large saucepan over low heat, combine the sugar, buttermilk, butter, baking soda, and vanilla and bring just to a boil, stirring constantly. Attach a candy thermometer to the pan, and continue to boil and stir until the mixture reaches 238 degrees F, 15 to 17 minutes. Remove the pan from the heat.
Dip each apple, one at a time, immediately into the caramel, leaving a 1/4-inch ring of green by the stick, and return the apple to the baking sheet. If the caramel starts to solidify while you are dipping apples, stir in heavy cream, a few drops at a time, until the caramel reaches a spreadable consistency.
After all the apples have been dipped, lightly sprinkle them with sea salt. Allow the caramel to set, about 5 minutes.
Meanwhile, in a microwave-safe bowl, microwave the white chocolate chips on high in 30-second intervals, stirring until melted. Dip each apple into the melted white chocolate, leaving a 1/4-inch ring of caramel exposed. Immediately dip the white chocolate-covered caramel apple in a layer of crushed cookie topping, leaving 1/4 inch of the white chocolate exposed.
Adding vinegar to milk makes buttermilk. You can use a different acidic component like lemon juice for the same effect. Use this tip when a recipe calls for buttermilk and you don't have any on hand.