Preheat the oven to 375 degrees F (190 degrees C). Line 2 cookie sheets with aluminum foil and grease the foil.
In a large skillet over medium heat, melt the butter. Stir together the oats, flour, salt and sugar; mix into the melted butter until well blended. Stir in the corn syrup, milk and vanilla. Drop batter by teaspoonfuls 3 inches apart onto the prepared cookie sheets.
Bake for 5 to 7 minutes in the preheated oven, until medium brown. Cool completely before removing from the cookie sheets. In the microwave or in a metal bowl over a pan of simmering water, melt chocolate chips, stirring frequently until smooth. Remove from heat. Spread chocolate onto the bottoms of cookies and sandwich them together.