1) To make 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.
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.
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.
6) To make 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.
7) To make 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 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.