These delicate, crisp cookies bake and freeze well for up to 2 months. Two tips: the cookies tend to stick and spread, so be sure to use a nonstick baking sheet liner or parchment and don't bake more than 12 cookies at a time.
Preheat oven to 325 degrees with rack in middle of the oven.
In a medium bowl, mix oats, sugar and melted butter together with a wooden spoon. Stir in egg until well blended, then add vanilla and orange juice. Add flour and salt and stir to mix. Batter will be somewhat thick.
On a lined baking sheet, drop batter by half-teaspoonfuls at least 2 inches apart and up to 12 cookies per sheet pan. Bake until golden brown, 8-10 minutes. Keep an eye on these, they will go from golden brown to burnt very quickly.
Cool cookies on baking sheet just until they hold their shape, about 2 minutes. Dont let completely cool or they will be difficult to remove. With a thin spatula, transfer them to a cool rack and let cool completely.
Melt chocolate in a microwave safe bowl for 30 seconds at a time stirring until melted. Spread a thin layer of chocolate on a cookie and top with another cookie. Let chocolate harden about 2 hours before storing.