Begin by preparing your apples. Wash your apples under hot water to remove any wax. Dry the apples throughly with a towel.
Pierce the apple with a caramel apple stick or popsicle stick, then place on a parchment-lined baking sheet.
Add the whipping cream and salted butter to a small pot and heat until it just begins to simmer. Do not boil. Once it is warm, remove from the heat and set aside.
In a large pot (>4 quarts), add the sugar, corn syrup and water. Use a whisk to gently mix to combine. Once combined, dip a pastry brush in a some water and brush down the sides of the pot so that there are no sugar crystals left on the sides of the pot. Do not stir the caramel until the next stage.
Place the pot over medium-high heat and insert a candy thermometer into the pot. Make sure that the tip of the thermometer is submerged in the sugar mixture or else you won't get a proper temperature reading. Let the sugar mixture come to a boil (without stirring). You will begin to see the mixture bubble after a few minutes and the mixture will turn from a clear colour to a toasty golden brown colour.
Once the sugar mixtures reaches 325 degrees F, remove the pot from the heat. Pour 1/4 cup of the warm cream and butter mixture into the sugar mixture. The caramel will bubble up quite a bit (which is why it's important to use a big pot) but don't be afraid of it. Add the remaining warm cream mixture in 1/4 cup increments. Once all the cream mixture has been added, gently whisk the mixture to combine.
Next, return the pot to the medium-high heat and let the caramel come to a boil. Do not stir the caramel anymore. You will see the caramel turn from a light brown to a dark red-brown. Bring the entire mixture to 245 degrees F (no higher) and remove from the heat. Next, add in the vanilla extract and whisk to combine.
Let the caramel cool for 5-7 minutes to firm up a bit. Then dip your apple into the caramel and rotate it in a circle to coast the sides. Once coated, place the caramel apple back on the parchment-lined baking sheet and let cool for 10 minutes.
After 10 minutes, garnish with a sprinkle of flaky sea salt. Enjoy!