1 1/2 cups heavy cream
1 cup sugar
1/2 cup brown sugar, packed
1/3 cup light corn syrup
1 tablespoon unsalted butter, plus extra for greasing dish
1 teaspoon salt
1 1/2 teaspoons vanilla extract
Sea salt, garnish
[Note: calibrate candy thermometer by attaching it to saucepan (making sure it’s not touching bottom of pan) and bring a large pot of water to boil for 10 minutes. Depending on your boiling point (which varies based on altitude, but standard is 212º F), check what the thermometer says when the water is at a full boil; if the thermometer reads under 212º F (or whatever the boiling point is typically for your region), make sure to add that many degrees to whatever you’re cooking so that it’s accurate. On the flip side, if your thermometer reads over 212º F when it’s at a rolling boil, make sure to subtract the difference in degrees from whatever it is you’re cooking.]
Line an 8-inch square baking dish with aluminum foil and lightly grease it with butter.
In a heavy-bottomed saucepan over medium heat, stir together heavy cream, sugars and corny syrup. Stir constantly so sugar dissolves and doesn’t burn; it will be thick.
Bring mixture to a boil, then dip your pastry brush in water and brush down the sides of your saucepan. Attach candy thermometer, just make sure that it doesn’t touch the bottom of the pan (which will give you an inaccurate temperature), and heat mixture to 245º F, swirling pan occasionally. 8-10 minutes. Mixture should be deep golden brown.
Remove pan from heat and season with salt, vanilla extract and butter, stirring continuously. Butter will cause mixture to spit and bubble, so be careful as you stir.
Once butter is incorporated, pour caramel into greased baking dish and sprinkle generously with sea salt. Let cool completely.
Once cool, lift caramel out of baking dish and peel away aluminum foil. Use a pizza cutter (lightly greased with non-stick spray, if desired), and cut caramels into squares or rectangles. Wrap with wax or parchment paper and store in an air-tight container. Enjoy!