Line an 8-inch square baking pan with aluminum foil, ensuring there's enough overhang on the sides for easy removal later. Lightly grease the foil with a bit of butter to prevent sticking.

In a 3-quart heavy duty saucepan, add the heavy cream, granulated sugar, light brown sugar, and light corn syrup. Over medium heat, stir constantly with a wooden spoon until the sugars dissolve.

Once the mixture boils, use a pastry brush dipped in water to brush down the sides of the pan to prevent sugar crystals from forming. Attach a candy thermometer to the pan, ensuring it doesn't touch the bottom.

Cook without stirring until the temperature hits 245°F (118°C), monitoring closely to avoid burning.

Remove from heat, then carefully stir in the salt, vanilla extract, vanilla bean seeds, and softened butter, taking caution as the mixture may bubble and burst.

Pour the hot caramel into the prepared baking pan and sprinkle with coarse sea salt if desired. Let it cool at room temperature, uncovered, for about 4 hours or overnight.

Once set, lift the caramel from the pan using the aluminum foil overhang. Cut into rectangles or squares with a sharp knife. Optionally wrap each piece in candy wrappers for gift-giving or storage.