1) Preheat the oven to 375°F. Get out your walnut cookie molds; there's no need to grease them.
2) To make the cookies: Beat the soft butter, brown sugar, salt, and flavorings until fluffy.
3) Stir in the flour, cornstarch, and nuts.
4) Wrap the dough, and refrigerate for 30 minutes.
5) Press 1 teaspoonful of chilled dough into the bottom and up the sides of each mold. Place the molds on a baking sheet.
6) Bake the cookies for 10 to 12 minutes, until they're browned around the edges. Cool for a few minutes, then push on the thick edge of each cookie to pop it out of the mold.
7) To make the filling: Heat the cream and corn syrup until steaming.; a microwave works well here.
8) Add the chocolate, stirring until it melts. Reheat briefly on low heat if the chocolate doesn't completely melt.
9) Cool until the mixture thickens somewhat, whisking often.
10) Spread a bit of the chocolate on each side of the cookies. Let them sit for a few minutes to partially set up, then sandwich the halves together.