I tried this recipe from Everyday Food (Oct. 2010) last night and they are goo-ood! If you don't have any Halloween chocolate left over you might still be able to get yourself a bag at a very good price.
1 cup unsalted butter, room temperature
3/4 cup packed light brown sugar
2 cups all purpose flour
1 cup semisweet chocolate chips
2 cups assorted chocolate candies or roughly chopped candy bars
Preheat oven to 350 degrees. With an electric mixer beat butter, brown sugar, and salt until light and fluffy. Add flour and beat on low speed until mixture is crumbly. Press dough into an 8 inch square baking dish. Bake until golden brown and firm, 30-35 minutes.
Scatter chocolate chips only on top of shortbread. Bake until soft, approx. 1 minute. Evenly spread melted chocolate chips over shortbread using the back of a a spoon. Scatter candies over top. Let cool on a wire rack 30 minutes. Refrigerate briefly to set the chocolate, then cut into bars.
These are very, very rich, but oh, so good! I would suggest using a slightly larger pan so you don't get so much shortbread in every piece. There's a lot of butter in there!
We used a combination of miniature Oh! Henry bars, Kit Kat, Coffee Crisp, Aero, Crispy Crunch and Reese's Pieces.
I guess I could have "styled" this photo a little better, but I was pretty excited to share the results with you. That, and I had to make sure to take a picture before any more of them got eaten!