I got this great recipe from here http://www.kingarthurflour.com/blog/2010/09/27/im-rich-im-rich-thousand-dollar-bars/ I did tweak it slightly to fit our dietary needs. While not quite "Twix" they still taste super great.
1 cup (2 sticks) salted butter, at room temperature
1 cup confectioners' sugar
2 teaspoons vanilla extract
2 cups white flour
2 cups caramel, cut into small chunks
3 tablespoons heavy cream
Attn. Those following the Feingold diet instead of doing the above for the caramel layer I made my own caramel sauce and you can get the recipe here http://arcticlilysloops.blogspot.com/2012/02/caramel-sauce.html The sauce was a little too thin for this purpose so I added some flour to thicken it up. You want it thin enough to be able to spread it but more of a honey consistency.
3 cups chopped milk or dark chocolate, melted (I used two cups semi - sweet Ghiradelli chocolate chips and two cups milk chocolate Ghiradelli chocolate chips.
1 tablespoon vegetable shortening (optional) (for those that know me you know I did not use shortening, I used coconut oil instead).
1) FOR THE CRUST: Preheat your oven to 300°F. Spray a 9" x 13" pan lightly with cooking spray, or line with parchment, and set aside (I lined with parchment paper).
2) In a medium-sized bowl, beat together the butter, sugar and vanilla. Add the flour. At first the mixture may seem dry, but will come together as you continue to beat at medium speed.
3) Take the dough (it will be somewhat stiff) and press it evenly into the pan. Lightly flouring your fingertips will help with any sticking. (To make it a little easier I took a drinking glass, coated it with a bit of oil and used it to help press it out.
4) Prick the crust all over with a fork. The holes will allow steam to escape and the crust will bake evenly with fewer bubbles.
5) Bake the crust until it's lightly golden brown on top and the edges are deeper golden brown, about 35 to 45 minutes. Remove from the oven and immediately run a knife around the edges to loosen the crust. Set it aside to cool completely. At 32 minutes this is what mine looked like and was a little too done so check it periodically!
6) FOR THE CARAMEL LAYER: Melt the caramel and cream over low heat in a small saucepan. Pour the caramel over the cooled crust and set in the refrigerator for 30 minutes to chill and firm up.
Attn: Feingold people, as stated before I did not make the caramel listed in the recipe but made my own and the link is in the list of ingredients above.
7) FOR THE CHOCOLATE LAYER: Melt the milk or dark chocolate slowly in a double boiler or over very low heat. If it seems very thick, add a tablespoon of shortening (coconut oil!) to thin it. Pour evenly over the chilled caramel layer and spread to cover all of the caramel. Return to the fridge until the chocolate is well set. Cut into 2" x 2" squares to serve. It's best to store these bars in the refrigerator.
8) These bars can also be cut and dipped in milk chocolate to resemble Twix ® bars. After the caramel layer has chilled firm, cut down the length of the pan, splitting the bars into two long, narrow bars. Then cut each long strip into "fingers". Dip the chilled bars into melted chocolate and place on parchment paper to set for several hours.
Okay so I thought I would try to cut them up into long bars and dip the whole thing in the chocolate like in step 8. This did not work out so well for me and after doing half that way, gave up and and just poured it over the other half like in step 7 and came out with bars looking like in the picture at the top of the page. If you want to save yourself trouble and mess that is what I suggest doing. Mine would kind of break as I was trying to dip them I think because the shortbread layer got too done, I still dipped the pieces and they still taste great but not going to go that route next time. This is how I cut them up, the the bars on the left are what I tried to dip in the chocolate and then the half on the right is what I decided to just pour the chocolate mixture over and let set in the fridge.