From Charity Ferreira.
You can control the final texture of these caramels by how long you cook them. Cook then at 245˚F (soft-ball stage) on your candy thermometer and they will be soft and chewy at room temperature. If you like them firmer, take them to 250˚F.
Yield: About 80 caramels
¾ cup (1 ½ stick) unsalted butter, plus more for pan
2 ¼ cups packed dark brown sugar
1 cup light corn syrup
1 cup whipping cream
½ cup water
1 tablespoon lemon juice
1 teaspoon salt
1 tablespoon vanilla extract
Step 1: Generously butter the sides of and bottom of an 8-inch square disposable aluminum pan. Place the pan on a baking sheet for stability.
Step 2: In a larger pot over medium-low heat, stir together the sugar, corn syrup, cream, ¾ cup butter, the water, the lemon juice, and salt until the sugar is dissolved and the butter is melted. Increase the heat and boil, stirring occasionally with a wooden spoon o a heatproof spatula, until the mixture is golden brown and measures 245˚F to 250˚F on a candy thermometer, 10 to 15 minutes. Remove from the heat and carefully (the mixture will bubble up) stir in the vanilla extract.
Step 3: Immediately pour the caramel into the prepared pan. Let stand at room temperature until top is set, about 20 minutes, then refrigerate (with baking sheet underneath) until firm enough to cut, about 2 ½ hours.
Step 4: Bend back the sides of the pan and invert to release the caramel onto a cutting board. Use a sharp knife to cut the caramel into 1-inch squares. Wrap each piece and store them in an airtight container in the refrigerator for up to 2 weeks. The caramels will taste best if you bring them to room temperature before eating.