Start by preheating your oven to 325º F. This step is essential because a properly heated oven ensures your shortbread crust will bake evenly and become golden brown.
Next, prepare the shortbread crust. In a mixing bowl, combine your butter, granulated sugar, and a pinch of sea salt. Beat until the mixture is light and fluffy, about two to three minutes. You'll know it's ready when it turns a pale yellow and has a creamy texture. This fluffy mixture forms the base of your bars.
Now, add in the flour to your butter mixture and mix until well combined. The dough should be soft but not sticky. Press this mixture evenly into the bottom of a 9 by 13-inch baking pan. Use your fingers or the bottom of a measuring cup to create an even layer.
Place the pan in the preheated oven and let it bake for about 15 to 20 minutes until the crust is set and lightly golden. Keep an eye on it; you want it just perfect, not overcooked! The aroma of baking butter will fill your kitchen.
While the crust cools, prepare the salted caramel layer. In a heavy-bottomed saucepan, combine the packed brown sugar, light corn syrup, butter, half and half, and sea salt. Stir over low to medium heat until everything is melted together.
Once melted, increase the heat to medium and allow the mixture to come to a gentle boil. Use a candy thermometer to monitor the temperature; you’re aiming for about 250º F, which is known as the hard ball stage. The caramel should turn a warm, golden brown color, signaling it's ready.
Remove the pan from heat and add in the vanilla extract. Be careful, as the mixture will bubble up! Stir vigorously with a wooden spoon until smooth and creamy.
Pour the caramel over the cooled shortbread crust, spreading it into an even layer. Let it sit at room temperature for about 10 minutes to set slightly.
Cover the pan with plastic wrap and refrigerate for at least 1 to 3 hours, or overnight if you can wait. This step is crucial to allow the caramel to firm up properly.
When ready to serve, remove the pan from the refrigerator. Let it sit at room temperature for about 20 minutes before slicing. This will make it easier to cut through the caramel.
