Preheat your oven to 300°F and line a 9" x 13" pan with parchment. This makes it easier to cut the bars later.
For the crust: In a medium-sized bowl, beat together the butter, confectioners' sugar, and vanilla. Add the flour and salt. Mixture will be dry but will come together after mixing.
Press dough evenly into the pan. Lightly flouring your fingertips will help with any sticking. Prick the crust all over with a fork to prevent bubbles.
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.
For the caramel layer: Melt the caramel and heavy cream in 30 second intervals in a microwave-safe bowl, stirring in between. This can also be done on the stove. Stir until smooth. Pour the caramel over the cooled crust and set in the refrigerator for 30 minutes to chill and firm up.
To make the chocolate layer: Melt the chocolate slowly in a double boiler or in the microwave in 30 second intervals. Add a tablespoon of shortening to thin it out if desired. 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. Let bars sit at room temperature for a couple of minutes to make cutting easier.
Store bars in the fridge. Caramel will soften at room temperature.
These bars can also be cut and dipped in melted chocolate to resemble Twix bars. After the caramel layer has chilled firm, cut into long strips, then dip into melted chocolate and place on parchment paper to set.
