Caramel Layer
Combine the butter, sugar, sweetened condensed milk, and corn syrup in a medium saucepan over medium heat.
Stir until butter is melted. Increasing to medium-high, bring the mixture to a boil.
Once it starts boiling, reduce it to a simmer - stirring constantly. The mixture will start to thicken, and lighten up.
Pour the caramel into a greased 9x13 bread pan. Chill in the refrigerator for at least 30 minutes.
Chocolate Layer
Add the chocolate, butter, and corn syrup in a heat-safe bowl.
Melt over a pan of hot water, until mixture is smooth and glossy.
Pour the chocolate over the chilled caramel.
Allow mixture to cool before sprinkling course sea salt over the top.
Serve chilled - this dessert melts easily!