Cookies

3⁄4 cup unsalted butter, softened
1 1⁄2 cups firmly packed dark brown sugar
1 large egg
2 tablespoons light corn syrup
3 cups quick-cooking oats (not instant)
1 cup all-purpose flour
1⁄2 teaspoon salt
1⁄2 teaspoon baking soda

Cream Filling

1⁄4 cup unsalted butter
2 tablespoons cream cheese, softened
1 cup confectioners’ sugar
1 cup marshmallow crème, such as Kraft

Caramel Filling

3⁄4 cup sugar
2 tablespoons water
2 tablespoons light corn syrup
3 tablespoons cold unsalted butter
1⁄4 teaspoon salt
1⁄2 cup heavy whipping cream