Preheat oven to 375 degrees and line several baking sheets with foil.
Melt butter in a medium saucepan. Remove from heat and stir in oats, sugar, flour, corn syrup, milk, vanilla extract, and salt.Use a teaspoon to measure out batter and space it 3 inches apart on prepared baking sheets. Spread each mound of batter out some with a rubber spatula.
Bake for 6 to 8 minutes or until golden brown. Place baking sheets on wire racks and let cookies sit until they are mostly cool, but still a little warm. Peel the foil off from the cookies.Note: You need to let the cookies cool enough so that they hold together when you peel the foil off, but I find that if you let them cool completely they sometimes get a little bit stuck to the foil.
Place chocolate chips in a medium microwave-safe bowl. Microwave at 20 second increments until completely melted when you stir.
Spread a layer of chocolate on the flat side of half the cookies. Top with remaining cookies.
Notes
Makes about 3 dozen cookies.Cookies will keep for 3 to 4 days at room temperature. Store them in an airtight container or ziptop bags.