In a large saucepan, combine 1 cup of unsalted butter, 2 cups of light brown sugar, 1/2 cup of light corn syrup, and 1 can of sweetened condensed milk over medium heat. Stir until the butter melts and the mixture is smooth, about 5 minutes.

Increase the heat to medium-high and stir constantly until it comes to a gentle boil, about 3–5 minutes.

Gradually stir in 1 cup of heavy whipping cream while monitoring temperature with a digital thermometer. The mixture should reach 225°F (107°C) after about 10 minutes.

Once it reaches 225°F, remove from heat and stir in 1 teaspoon of vanilla extract and a pinch of fine salt.

Pour the hot caramel filling into a heat-resistant container and let it cool at room temperature for approximately 30 minutes.

Store in an airtight container; it can last at room temperature for 2 days or in the refrigerator for up to a month.