For Shortbread: 2 cups (1 lb or 4 sticks) butter, softened 1 cup sugar 1/4 cup light brown sugar, packed 3 3/4 cup all-purpose flour 1/2 teaspoon salt For Caramel: 2 cups sugar 12 tablespoons butter 1 cup heavy cream 1 tbsp fleur de sel or fine sea salt For Cookie Dough: 1 cup (2